Folded access line for memory cell access in a memory device

ABSTRACT

Systems, methods, and apparatus related to spike current suppression in a memory array. In one approach, a memory device includes a memory array having a crosspoint memory architecture. The memory array has access lines (e.g., word lines and/or bit lines) configured to access memory cells of the memory array. Spike current suppression is implemented using a folded access line structure. Each access line includes integrated top and bottom insulating layers that restrict current flow to the memory cells through a narrower middle portion of the access line. For near memory cells located overlying or underlying the insulating layers, the resistance to each memory cell is increased because the cell is accessed using only the higher resistance path of the meandering, folded circuit path that flows through the middle portion. Spike discharge that occurs when the memory cell is selected is reduced by this higher resistance path.

FIELD OF THE TECHNOLOGY

At least some embodiments disclosed herein relate to memory devices ingeneral, and more particularly, but not limited to a folded access linestructure for spike current suppression in a memory array.

BACKGROUND

Memory devices are widely used to store information in variouselectronic devices such as computers, wireless communication devices,cameras, digital displays, and the like. Information is stored byprograming memory cells within a memory device to various states. Forexample, binary memory cells may be programmed to one of two supportedstates, often denoted by a logic 1 or a logic 0. In some examples, asingle memory cell may support more than two states, any one of whichmay be stored. To access the stored information, a component may read,or sense, at least one stored state in the memory device. To storeinformation, a component may write, or program, the state in the memorydevice.

Various types of memory devices and memory cells exist, includingmagnetic hard disks, random access memory (RAM), read-only memory (ROM),dynamic RAM (DRAM), synchronous dynamic RAM (SDRAM), ferroelectric RAM(FeRAM), magnetic RAM (MRAM), resistive RAM (RRAM), flash memory, phasechange memory (PCM), self-selecting memory, chalcogenide memorytechnologies, and others. Memory cells may be volatile or non-volatile.Non-volatile memory devices (e.g., FeRAM) may maintain their storedlogic state for extended periods of time even in the absence of anexternal power source. Volatile memory devices (e.g., DRAM) may losetheir stored state when disconnected from an external power source.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which like referencesindicate similar elements.

FIG. 1 shows a memory device that implements spike current suppressionin a memory array, in accordance with some embodiments.

FIG. 2 shows resistors used to implement spike current suppression foran access line of a memory array, in accordance with some embodiments.

FIG. 3 shows an access line split into left and right portions for spikecurrent suppression, in accordance with some embodiments.

FIG. 4 shows a memory array in a cross-point architecture includingvarious word line and bit line layers that provide access to memorycells arranged in multiple stacked decks, in accordance with someembodiments.

FIG. 5 shows word lines in a memory array electrically connected by avia, in accordance with some embodiments.

FIG. 6 shows a memory device configured with drivers to generatevoltages on access lines of a memory array, in accordance with someembodiments.

FIG. 7 shows a memory cell with a bit line driver to generate a voltageon a bit line, and a word line driver to generate a voltage on a wordline, in accordance with some embodiments.

FIG. 8 shows an example of a memory cell that includes a select device,in accordance with some embodiments.

FIGS. 9-12 show various steps in the manufacture of a memory device thatimplements spike current suppression, in accordance with someembodiments.

FIG. 13 shows a method for manufacturing a memory device that implementsspike current suppression, in accordance with some embodiments.

FIG. 14 shows an access line having two resistive films, and a socket inwhich a conductive layer is formed, for spike current suppression, inaccordance with some embodiments.

FIGS. 15-21 show steps in the manufacture of a memory device thatimplements spike current suppression by forming two resistive films inan access line, and a conductive layer in a socket of the access line,in accordance with some embodiments.

FIG. 22 shows a method for manufacturing a memory device that implementsspike current suppression by forming two resistive films and aconductive layer in a socket, in accordance with some embodiments.

FIGS. 23 and 24 show steps in the manufacture of a memory device thatimplements spike current suppression by forming a resistive layer in asocket, in accordance with some embodiments.

FIG. 25 shows a method for manufacturing a memory device that implementsspike current suppression by forming a resistive layer in a socket, inaccordance with some embodiments.

FIG. 26 shows an access line having charge screening structures that areused for spike current suppression, in accordance with some embodiments.

FIG. 27 shows an access line having insulating layers located ininterior regions of the access line and used for spike currentsuppression, in accordance with some embodiments.

FIGS. 28-32 show steps in the manufacture of a memory device thatimplements spike current suppression by forming one or more chargescreening structures in an access line, in accordance with someembodiments.

FIG. 33 shows a cross-sectional view of the access line and memory arrayof FIG. 32 .

FIG. 34 shows a method for manufacturing a memory device that implementsspike current suppression using one or more charge screening structuresin an access line, in accordance with some embodiments.

FIG. 35 shows an access line having multiple insulating layers locatedin an interior region of the access line and used for spike currentsuppression, in accordance with some embodiments.

FIG. 36 shows a folded access line structure used for spike currentsuppression in a memory array of a memory device, in accordance withsome embodiments.

FIGS. 37-45 show steps in an approach for the manufacture of a memorydevice that implements spike current suppression using a folded accessline structure in a memory array, in accordance with some embodiments.

FIGS. 46-53 show steps in another approach for the manufacture of amemory device that implements spike current suppression using a foldedaccess line structure in a memory array, in accordance with someembodiments.

FIG. 54 shows a method for manufacturing a memory device that implementsspike current suppression using a folded access line structure in amemory array, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure describes various embodiments for spike currentsuppression in a memory array. At least some embodiments herein relateto a memory device having a memory array that uses a cross-pointarchitecture. In one example, the memory array is a resistive RAM (RRAM)cross-point memory array, or a ferroelectric RAM (FeRAM) cross-pointmemory array. Other memory types may be used.

In one example, the memory device stores data used by a host device(e.g., a computing device of an autonomous vehicle, an artificialintelligence (AI) engine, or other computing device that accesses datastored in the memory device). In one example, the memory device is asolid-state drive mounted in an electric vehicle.

In some memory arrays (e.g., a cross-point memory array), currentdischarges through a memory cell may result in current spikes (e.g.,relatively high current discharge through the memory cell in arelatively short time period), which may cause damage to the memorycell. For example, current discharge that occurs when a chalcogenidememory cell snaps can result in amorphization of the memory cell. Suchspikes may result from internal discharge within the memory array. Inone example, this is the discharge of parasitic capacitances within thememory array. Current spikes due to internal discharge may beparticularly problematic.

In one example, memory cells are selected by generating voltages on wordand bit lines of the memory array. When the memory cell is selected, alarge current spike can flow through the cell. The spike is caused byparasitic capacitances that have accumulated charge during operation ofthe memory device. The charge is discharged as a current spike that cancause damage to the memory cell.

In one example, the memory cell is a chalcogenide-based self-selectingmemory cell that snaps when selected (e.g., the cell is in a SET state).A selection spike results from discharge of parasitic capacitancescoupled to the word and/or bit line that are used to select the memorycell. Memory cells that use both a select device and a memory storageelement (e.g., phase change memory) can suffer from similar problems.

This selection spike can be a root cause of several reliabilitymechanisms. This is particularly true for memory cells that are locatednear a decoder, for which spike current is typically greater. Forexample, the selection spikes cause reliability mechanisms such as readdisturb and/or endurance degradation.

In one example, various voltages of a memory array may be altered toperform access operations. The various voltage alterations may causecharge in the memory array to build up, for example, in the parasiticcapacitances associated with the array (e.g., the parasitic capacitancesof the access lines of the memory array). In some cases, the built-upcharge may discharge through a selected memory cell. For example, amemory cell may become conductive based on being selected (e.g., whenaccessed, such as when a voltage across the memory cell crosses athreshold voltage of the memory cell), which may allow built-up chargeon the access lines coupled with the memory cell to discharge throughthe cell in a current spike (e.g., a current spike having a peakmagnitude of at least 100 microamps, such as 200-300 microamps). Thememory cell may be degraded or worn out in proportion to the number andmagnitude of current spikes experienced by the memory cell over time.

In one example, a memory array uses self-selecting chalcogenide memorycells. As cells are selected, word and bit lines are charged up toselect the cells. This can cause capacitive coupling to adjacent word orbit lines for adjacent cells. Over time, this capacitive coupling causeselectrical charge to accumulate in various parasitic capacitances (e.g.,such as mentioned above). When the memory cell is selected and snaps(e.g., during a read operation), the accumulated electrical charge flowsthrough the memory cell as a current spike.

In some cases, current spikes may be higher for memory cells locatedclose or near to a via that connects to an access line driver (e.g., anear electrical distance (ED)) than for memory cells located far fromthe via/driver (e.g., a far ED). For example, discharge through a memorycell with a near ED may be more severe due to a relatively lowerresistance path between the memory cell and the charge built up inparasitic capacitances along the entire length of the access line, whichmay result in a higher amount of current through the memory cell whenthe memory cell becomes conductive (e.g., a relatively higher magnitudecurrent spike) than for memory cells with far ED, which may be moreseparated from charge built up along farther away portions of the accessline (e.g., charge built up far along the access line on the other sideof the via).

To address these and other technical problems, one or more resistors areused to screen electrical discharge from portions of an access lineother than the portion being used to access a memory cell. The screeningof the electrical discharge by the one or more resistors reduces theextent of electrical discharge that would occur in the absence of theresistors (e.g., the lack of such resistors in prior devices).

The physical configuration of the resistors can be customized depending,for example, on the location of the access line in a memory array. Inone example, each resistor is a portion of a resistive film locatedbetween the access line and a via that is electrically connected to adriver used to drive voltages on the access line when selecting thememory cell.

In one example, the access line is a word line of a cross-point memoryarray. The one or more resistors are configured to increase theresistance of a circuit path through which parasitic capacitance(s) ofthe cross-point memory array may discharge so that the magnitude of anycurrent spike is reduced. The magnitude of the current spike is lower ascompared to prior approaches in which the resistors are not used (e.g.,the resistors increase the resistance of the RC discharge circuit, whichreduces the current spike). Also, the use of the one or more resistorshas minimal impact on the ability to bias and deliver current to theword line for normal memory cell operations such as reading, writing,etc.

In one embodiment, an access line is split into left and right portions(e.g., left and right word line or bit line portions). Each portion iselectrically connected to a via, which a driver uses to generate avoltage on the access line. To reduce electrical discharge associatedwith current spikes, a first resistor is located between the leftportion and the via, and a second resistor is located between the rightportion and the via.

In some embodiments, spike current suppression is implemented by using asocket structure that is formed in an access line, as discussed in moredetail below (see, e.g., FIG. 14 and the related discussion below). Inone embodiment, a socket of the access line is filled with a conductivelayer, and two resistive films are formed in the access line on eachside of the conductive layer.

In other embodiments, spike current suppression is implemented by usingone or more charge screening structures, as discussed in more detailbelow (see, e.g., FIGS. 26 and 27 , and the related discussion below).In one embodiment, the charge screening structures are formed byintegrating insulating layers into interior regions of an access line(e.g., insulating layers extending laterally in the middle of certainportions of the access line). The insulating layers vertically split theaccess line into top and bottom conductive portions. For those memorycells that are located overlying and/or underlying one of the insulatinglayers, the resistance of the electrical path to each memory cell isincreased because the thickness of the top or bottom conductive portionis less than the thickness of those portions of the access line wherethe insulating layers are not present. Thus, during a spike discharge,charge is choked by the higher resistance path to the memory cell. Forexample, this suppresses spike current that may occur when one of theoverlying and/or underlying memory cells is selected (e.g., achalcogenide memory cell snaps).

One advantage of the charge screening structure is that via resistancedoes not need to be increased, so that delivery of current to memorycells located far from the via is minimally affected. For example, thetop and bottom conductive portions are both used for far currentdelivery, such that the combined electrical paths have a resistance thatis substantially similar to that of the portions of the access linewithout insulating layers.

In one embodiment, a memory device includes a memory array having across-point memory architecture. The memory array has an access lineconfigured to access memory cells of the memory array. The access linehas a first portion and a second portion on opposite sides of a centralregion of the access line. The first portion is configured to access afirst memory cell, and the second portion configured to access a secondmemory cell. In one example, the access line is a word line or bit line,and the central region is in the middle of the word or bit line. In oneexample, the access line is split into left and right portions asmentioned above.

One or more vias are electrically connected at the central region to thefirst portion and the second portion. In one example, a single via isused. In other examples, multiple vias can be used.

A first resistor is located between the first portion of the access lineand the via. The first resistor is configured so as to screen electricaldischarge from the first portion when accessing the second memory cell.A second resistor is located between the second portion and the via. Thesecond resistor is configured to screen electrical discharge from thesecond portion when accessing the first memory cell.

A driver is electrically connected to the one or more vias. The driveris configured to generate a voltage on the first portion when accessingthe first memory cell. The driver generates a voltage on the secondportion when accessing the second memory cell. In one example, thedriver is a word line or bit line driver. In one example, the driver iselectrically connected to a single via in the middle of a word line, anda voltage is generated on both the first and second portions whenaccessing a single memory cell. The memory cell can be located on eitherthe first or second portion.

Various advantages are provided by embodiments described herein. In oneadvantage, current spikes that result during selection of a memory cellare suppressed by screening charge from far capacitances in a memoryarray (e.g., charge from far cells on a left portion of an access linein a left half tile used to access a near memory cell, and/or chargefrom a right portion of the access line in the right half tile). In oneadvantage, the resistors above can readily be added on an existing quiltarchitecture.

In one advantage, use of the resistors above can be varied for differentlocations of the memory array. The layers used to form the memory cellstack can be the same for all portions of the memory array. Thus, theuse of the spike current suppression as described herein can betransparent to memory cell structure.

In one advantage, for a given level of tolerable current spike, tilesize and thus memory density can be increased. In one advantage, variousdifferent resistor configurations can be combined and varied as desiredfor different portions of a memory array. In one advantage, the spikecurrent suppression can be generally used for any cross-pointtechnology.

FIG. 1 shows a memory device 101 that implements spike currentsuppression in a memory array 102 of memory device 101, in accordancewith some embodiments. Memory device 101 includes memory controller 120,which controls sensing circuitry 122 and bias circuitry 124. Memorycontroller 120 includes processing device 116 and memory 118. In oneexample, memory 118 stores firmware that executes on processing device116 to perform various operations for memory device 101. In one example,the operations include reading and writing to various memory cells ofmemory array 102.

The memory cells of memory array 102 include memory cells 110 and memorycells 112. In one example, memory cells 110 are located in a left halftile and memory cells 112 are located in a right half tile of the memoryarray.

Access lines 130 of memory array 102 are used to access memory cells110, 112. In one example, access lines 130 are word lines and/or bitlines. In one example, each access line 130 is split in a central region(e.g., the middle of the access line) to have a left portion thataccesses memory cells 110 and a right portion that accesses memory cells112.

Bias circuitry 124 is used to generate voltages on access lines 130.Vias 134 are used to electrically connect access lines 130 to biascircuitry 124. In one example, a single via 134 is used to electricallyconnect a left portion and a right portion of each access line 130 to aword or bit line driver of bias circuitry 124.

In one example, a voltage is driven on a left portion of an access line130 to access a memory cell 110. In one example, the voltage is drivenas part of a read or write operation performed in response to a commandreceived from host device 126.

Sensing circuitry 122 is used to sense current flowing through memorycells 110, 112. In one example, sensing circuitry 122 senses a currentthat results from applying a voltage to a memory cell 110 during a readoperation.

In one embodiment, in order to suppress spike currents in memory array102, various resistors 132 are located between access lines 130 and vias134. The resistors 132 screen electrical discharge (e.g., as describedabove) from certain portions of access lines 130 that can occur when amemory cell 110, 112 is accessed (e.g., when a chalcogenide memory cellsnaps).

In one embodiment, memory device 101 selects write voltages for applyingto memory cells 110, 112 when performing write operations. In oneembodiment, bias circuitry 124 is implemented by one or more voltagedrivers. Bias circuitry 124 may further be used to generate readvoltages for read operations performed on memory array 102 (e.g., inresponse to a read command from host device 126).

In one embodiment, sensing circuitry 122 is used to sense a state ofeach memory cell in memory array 102. In one example, sensing circuitry122 includes current sensors (e.g., sense amplifiers) used to detect acurrent caused by applying various read voltages to memory cells inmemory array 102. Sensing circuitry 122 senses a current associated witheach of the memory cells 110 caused by applying the voltage.

In one example, if sensing circuitry 122 determines that the respectivecurrent resulting from applying a read voltage to the memory cell isgreater than a respective fixed threshold (e.g., a predetermined levelof current or threshold current), then memory controller 120 determinesthat the memory cell has snapped.

In one embodiment, memory cells 110, 112 can be of different memorytypes (e.g., single level cell, or triple level cell).

In one embodiment, memory controller 120 receives a write command from ahost device 126. The write command is accompanied by data (e.g., userdata of a user of host device 126) to be written to memory array 102. Inresponse to receiving the write command, controller 120 initiates aprogramming operation by applying voltages to memory cells 110.Controller 120 determines respective currents resulting from applyingthe voltages.

In one embodiment, controller 120 determines whether the existingprogramming state (e.g., logic state zero) and the target programmingstate (e.g., logic state zero) for each cell are equal. If the existingand target programming states are equal, then no write voltage isapplied (e.g., this is a normal write mode). If the existing and targetprogramming states are different, then a write voltage is applied tothat particular memory cell. In one example, the write voltage is 3-8volts applied across the memory cell by applying voltage biases to theword line and bit line used to select the cell.

In one example, controller 120 may use write voltages (e.g., writepulses) to write a logic state to a memory cell, such as memory cell110, 112 during the write operation. The write pulses may be applied byproviding a first voltage to a bit line and providing a second voltageto a word line to select the memory cell. Circuits coupled to accesslines to which memory cells may be coupled may be used to provide thewrite voltages (e.g., access line drivers included in decoder circuits).The circuits may be controlled by internal control signals provided by acontrol logic (e.g., controller 120). The resulting voltage applied tothe memory cell is the difference between the first and second voltages.

In some cases, the memory cell (e.g., a PCM cell) includes a materialthat changes its crystallographic configuration (e.g., between acrystalline phase and an amorphous phase), which in turn, determines athreshold voltage of the memory cell to store information. In othercases, the memory cell includes a material that remains in acrystallographic configuration (e.g., an amorphous phase) that mayexhibit variable threshold voltages to store information.

FIG. 2 shows resistors 210, 212 used to implement spike currentsuppression for an access line of a memory array, in accordance withsome embodiments. The access line has a first portion 202 and a secondportion 204 (e.g., left and right portions as described above). Theaccess line of FIG. 2 is an example of an access line 130 of memoryarray 102. Portion 202 is used to access memory cell 206, and portion204 is used to access memory cell 208. Each portion 202, 204 istypically used to access multiple memory cells (e.g., memory cellslocated in the memory array above and below the respective portion).

Access line portions 202, 204 are electrically connected to via 214 byresistors 210, 212. In one example, access line portions 202, 204 areportions of a conductive layer in a memory array. In one example,resistors 210, 212 are portions of a resistive film formed underlyingthe conductive layer and overlying via 214.

In one example, via 214 is a single via. In one example, via 214 isprovided by multiple vias. Via 214 electrically connects driver 216 toaccess line portions 202, 204. Driver 216 is an example of biascircuitry 124. In one example, driver 216 generates a read voltage onportion 202 in order to determine a state of memory cell 206. In oneexample, driver 216 generates a read voltage on portion 204 in order todetermine a state of memory cell 208.

Memory cells 206, 208 may be formed using various memory cell types. Inone example, the memory cell includes chalcogenide. In one example, thememory cell includes a select device, and a phase change material as amemory element. In one example, the memory cell is a self-selectingmemory cell including chalcogenide. In one example, the memory cell is aresistive memory cell.

FIG. 3 shows an access line split into left and right portions 302, 304for spike current suppression, in accordance with some embodiments. Leftportion 302 is used to access memory cell 308, and right portion 304 isused to access memory cell 310. The access line provided by portions302, 304 is an example of an access line 130 of FIG. 1 , or the accessline of FIG. 2 .

In one embodiment, a split in the access line is provided in a centralregion 306 of the access line. In one example, the split is formed inthe middle of the access line so that portions 302 and 304 are patternedto have substantially equal or identical lengths. In one example,portions 302 and 304 are patterned to have different lengths.

Left and right portions 302, 304 are electrically connected to via 312by a resistive film 318. Resistive film 318 has a section 320 locatedbetween left portion 302 of the access line and via 312. Resistive film318 has a section 322 located between right portion 304 of the accessline and via 312.

In one example, each of sections 320, 322 has a thickness of 1 to 20nanometers. In one example, each of sections 320, 322, has a width of 10to 200 nanometers. The width is indicated in FIG. 3 by the arrowscorresponding to reference numbers 320, 322.

In one example, resistive film 318 includes tungsten silicon nitride. Inone example, resistive film 318 includes one or more of tungsten siliconnitride, titanium silicide nitride, tungsten nitride, titanium nitride,tungsten silicide, or cobalt silicide. The proportions of the foregoingmaterials can be varied for different memory arrays.

In one embodiment, the split is a gap that physically separates portions302, 304. In one example, the split includes a non-conductive materialformed in central region 306 between portions 302 and 304. In oneexample, the non-conductive material is an insulating oxide. In oneexample, the split is an unfilled space between portions 302, 304.

Via 312 is electrically connected to transistor circuitry 316, which isformed in a semiconductor substrate 314. In one example, transistorcircuitry 316 includes bias circuitry 124. In one example, transistorcircuitry 316 includes one or more voltage drivers to generate voltageson portions 302, 304 of the access line shown in FIG. 3 . In oneexample, transistor circuitry 316 is formed using CMOS transistors.

FIG. 4 shows a memory array in a cross-point architecture includingvarious word line and bit line layers that provide access to memorycells arranged in multiple stacked decks, in accordance with someembodiments. The memory array includes various word lines and bit linesarranged orthogonally (e.g., perpendicularly) to one another. Forexample, word lines 412, 414 are arranged perpendicularly to bit lines406, 408. Word lines 412, 414 are an example of access lines 130 of FIG.1 . Additionally and/or alternatively, bit lines 406, 408 are an exampleof access lines 130.

The memory array includes various memory cells arranged in various decks(e.g., Decks 0-3). Each deck includes memory cells. For example, Deck 0includes memory cells 402, and Deck 1 includes memory cells 404. Memorycells 402, 404 are an example of memory cells 110. In one embodiment,each bit line 406 provides access to memory cells 402, 404, which arelocated above and below the respective bit line.

Although not shown for purposes of simplified illustration, each of wordlines 412, 414 may incorporate resistors 210, 212 described above. Inone example, each of word lines 412, 414 is split to have a left portion302 and a right portion 304, similarly as discussed above. In oneexample, each word line and/or bit line for any or all of the Decks 0-3can include a split, such as discussed above for FIG. 3 . In oneexample, various configurations of resistors 210, 212 can be used fordifferent word lines and/or bit lines. In one example, the configurationfor resistors 210, 212 is determined based on an extent of electricaldischarge associated with a given region of the memory array.

In one embodiment, word line 412 is electrically connected to word line414 by via 410. Via 410 is an example of via 134, 214, 312.

Although not shown for purposes of simplified illustration, via 410 iselectrically connected to a driver used to generate a voltage on wordlines 412, 414. In one example, the driver is bias circuitry 124 ordriver 216.

FIG. 5 shows word lines in a memory array electrically connected by avia, in accordance with some embodiments. In one embodiment, a word linethat provides access to memory cells in a top deck of the memory arrayhas left and right portions 502, 504, which are separated by a split506. Left and right portions 502, 504 are an example of left and rightportions 302, 304. Word line 520 provides access to memory cells in abottom deck of the memory array.

In one embodiment, a via electrically connects left and right portions502, 504 to word line 520. In one example, the via includes conductiveportions 508, 510, 512, which are electrically connected by via 514 to adriver (not shown). In one example, each of conductive portions 508,510, 512 corresponds to a conductive layer that is patterned and formedusing, for example, a photoresist layer when manufacturing the memoryarray. In one example, conductive portion 510 is a landing pad forconductive portion 508.

In one embodiment, resistive film 530 electrically connects left andright portions 502, 504 to conductive portion 508. Resistive film 530 isan example of resistive film 318.

In one embodiment, a split (not shown) may be formed above via 514 incentral region 522 of word line 520. Word line 520 is an example of wordline 414.

FIG. 6 shows a memory device configured with drivers to generatevoltages on access lines of a memory array 333, in accordance with someembodiments. For example, memory cells 206, 208 illustrated in FIG. 2can be used in the memory cell array 333.

The memory device of FIG. 6 includes a controller 331 that operates bitline drivers 337 and word line drivers 335 to access the individualmemory cells (e.g., 206, 208) in the array 333. Controller 331 is anexample of memory controller 120. Memory array 333 is an example ofmemory array 102.

The bit line drivers 337 and/or the word line drivers 335 can beimplemented by bias circuitry 124. In one example, each memory cell(e.g., 206, 208) in the array 333 can be accessed via voltages driven bya pair of a bit line driver and a word line driver, as illustrated inFIG. 7 .

FIG. 7 shows a memory cell 401 with a bit line driver 447 to generate avoltage on a bit line (wire 441), and a word line driver 445 to generatea voltage on a word line (wire 443), in accordance with someembodiments. For example, the bit line driver 447 drives a first voltageapplied to a row of memory cells in the array 333; and the word linedriver 445 drives a second voltage applied to a column of memory cellsin the array 333. A memory cell 401 in the row and column of the memorycell array 333 is subjected to the voltage difference between the firstvoltage driven by the bit line driver 447 and the second voltage drivenby the word line driver 445. When the first voltage is higher than thesecond voltage, the memory cell 401 is subjected to one voltage polarity(e.g., positive polarity); and when the first voltage is lower than thesecond voltage, the memory cell 401 is subjected to an opposite voltagepolarity (e.g., negative polarity).

For example, when the memory cell 401 is configured to be read withpositive voltage polarity, the bit line driver 447 can be configured todrive a positive voltage. For example, when the memory cell 401 isconfigured to be read with negative voltage polarity, the word linedriver 445 can be configured to drive a positive voltage.

For example, during the write operation, both the bit line driver 447and the word line driver 445 can drive voltages of differing magnitudes(e.g., to perform read or write steps). For example, the bit line driver447 can be configured to drive a positive voltage with differingmagnitudes; and the word line driver 445 can be configured to drive anegative voltage with differing magnitudes. The difference between thevoltage driven by the bit line driver 447 and the voltage driven theword line driver 445 corresponds to the voltage applied on the memorycell 401.

In one example, the bit line drivers 337 can be used to drive parallelwires (e.g., 441) arranged in one direction and disposed in one layer ofcross-point memory; and the word line drivers 435 can be used to driveparallel wires (e.g., 443) arranged in another direction and disposed inanother layer of a cross-point memory. The wires (e.g., 441) connectedto the bit line drivers (e.g., 447) and the wires (e.g., 443) connectedto the word line drivers (e.g., 445) run in the two layers in orthogonaldirections. The memory cell array 333 is sandwiched between the twolayers of wires; and a memory cell (e.g., 401) in the array 333 isformed at a cross point of the two wires (e.g., 441 and 443) in theintegrated circuit die of the cross-point memory.

FIG. 8 shows an example of a memory cell that includes a select device610, in accordance with some embodiments. In one example, select device610 includes a chalcogenide. Memory cell 602 is an example of memorycells 110, 112; or memory cells 206, 208.

Top electrode 608 conductively connects select device 610 to bit line604, and bottom electrode 612 conductively connects select device 610 toword line 606. In one example, electrodes 608, 612 are formed of acarbon material. Bit line 604 and word line 606 are each an example ofan access line 130. In one example, word line 606 and/or bit line 604 issplit into left and right portions 302, 304 as described herein.

In one example, select device 610 includes a chalcogenide (e.g.,chalcogenide material and/or chalcogenide alloy). Threshold voltageproperties of the select device may be based on the voltage polaritiesapplied to the memory cell.

In one example, a logic state may be written to memory cell 602, whichmay correspond to one or more bits of data. A logic state may be writtento the memory cell by applying voltages of different polarities atdifferent voltage and/or current magnitudes. The memory cell may be readby applying voltages of a single polarity. The writing and readingprotocols may take advantage of different threshold voltages of theselect device that result from the different polarities. Thechalcogenide material of the select device may or may not undergo aphase change during reading and/or writing. In some cases, thechalcogenide material may not be a phase change material.

In one embodiment, an apparatus includes: a memory array (e.g., 102,333) including an access line (e.g., 130) configured to access memorycells (e.g., 206, 208; 308, 310) of the memory array, the access linehaving a first portion (e.g., 202, 302) and a second portion (e.g., 204,304) on opposite sides of a central region (e.g., 306) of the accessline, where the first portion is configured to access a first memorycell, and the second portion configured to access a second memory cell;at least one via (e.g., 214, 312) electrically connected at the centralregion to the first portion and the second portion; a first resistor(e.g., 210) located between the first portion and the via, where thefirst resistor is configured to screen electrical discharge from thefirst portion when accessing the second memory cell; a second resistor(e.g., 212) located between the second portion and the via, where thesecond resistor is configured to screen electrical discharge from thesecond portion when accessing the first memory cell; and a driver (e.g.,216) electrically connected to the via, where the driver is configuredto generate a voltage on the first portion to access the first memorycell, and to generate a voltage on the second portion to access thesecond memory cell.

In one embodiment, the at least one via is a single via; the access lineis a bit line or a word line; and the driver is a bit line driver or aword line driver.

In one embodiment, the first resistor is provided by a first section(e.g., 320) of a resistive film (e.g., 318) overlying the via; and thesecond resistor is provided by a second section (e.g., 322) of theresistive film overlying the via. The central region includes a split inthe access line overlying the via and between the first and secondportions of the access line.

In one embodiment, the resistive film includes tungsten silicon nitride.

In one embodiment, the split is formed by removing a third portion ofthe access line to physically separate the first portion from the secondportion; and prior to removing the third portion, the third portion islocated between the first portion and the second portion.

In one embodiment, the split includes: a non-conductive materialconfigured to inhibit current discharge from flowing directly betweenthe first and second portions of the access line; or an unfilled spacebetween the first portion and the second portion.

In one embodiment, the memory array is part of a memory device (e.g.,101); the access line is associated with a physical address within thememory array; and an access operation by a controller (e.g., 120) of thememory device to select the first memory cell addresses both the firstand second portions of the access line.

In one embodiment, an apparatus includes: an access line having a firstportion (e.g., 302) and a second portion (e.g., 304), where the firstportion is configured to access a memory cell (e.g., 308) of a memoryarray, and a gap physically separates the first portion and the secondportion; a via (e.g., 312) electrically connected to the first portionand the second portion; and a resistive film (e.g., 318) having a firstsection between the first portion and the via, and a second sectionbetween the second portion and the via.

In one embodiment, the apparatus further includes a driver (e.g., adriver in transistor circuitry 316) electrically connected to the via,where the driver is configured to generate a voltage on the firstportion to access the memory cell.

In one embodiment, the gap is a split in the access line formed byremoving a third portion of the access line to physically separate thefirst portion of the access line from the second portion.

In one embodiment, a material forming the resistive film has a higherresistivity than a material forming the first and second portions of theaccess line.

In one embodiment, the resistive film includes at least one of: tungstensilicon nitride; titanium silicide nitride; tungsten nitride; titaniumnitride; tungsten silicide; or cobalt silicide.

In one embodiment, each of the first and second portions is configuredto access memory cells located above and below the respective portion.

In one embodiment, the memory array has a cross-point architecture, andthe memory cell is: a memory cell including chalcogenide; a memory cellincluding a select device, and a phase change material as a memoryelement; a self-selecting memory cell including chalcogenide (e.g.,memory cell 602); or a resistive memory cell.

In one embodiment, the gap overlies a third section of the resistivefilm (e.g., the middle section of resistive film 318 located undercentral region 306), and the third section is positioned between thefirst section and the second section.

FIGS. 9-12 show various steps in the manufacture of a memory device thatimplements spike current suppression, in accordance with someembodiments. In one example, the memory device is memory device 101.

FIG. 9 shows a memory array 902 at an intermediate stage of manufacture.Memory array 902 includes various memory cells 908. Each memory cell 908includes a memory stack containing various layers of materials (e.g.,chalcogenide, phase change material, etc.) corresponding to the memorycell technology that has been chosen for use. Memory cells 908 are anexample of memory cells 110, 112; memory cells 206, 208; or memory cells308, 310.

Memory array 902 includes a via 904 that has been formed on a pad 906.Memory array 902 as shown in FIG. 9 can be formed using conventionalmanufacturing techniques.

As shown in FIG. 10 , a nitride layer 1010 is formed overlying a topsurface of memory array 902. In one example, nitride layer 1010 includesone or more of tungsten silicon nitride, titanium silicide nitride,tungsten nitride, or titanium nitride. In one example, one or more oftungsten silicide or cobalt silicide can be alternatively oradditionally used. The proportions of the foregoing materials can bevaried for different memory arrays.

A word line 1012 is formed overlying nitride layer 1010. In one example,word line 1012 is a conductive material. In one example, word line 1012is tungsten.

As shown in FIG. 11 , a hard mask 1102 is formed overlying word line1012. Then, a photoresist layer 1104 is formed overlying hard mask 1102.

As shown in FIG. 12 , photoresist layer 1104 is patterned and used toetch hard mask 1102, word line 1012, and nitride layer 1010 to provideopening 1202 overlying via 904. In one example, a tungsten-only etch isused.

After the above etch, photoresist layer 1104 and hard mask 1102 areremoved. Subsequent manufacture of the memory device can be performedusing conventional manufacturing techniques.

Providing the opening 1202 splits word line 1012 into left and rightportions. In one example, these portions correspond to left and rightportions 302, 304.

In one example, the remaining portion of nitride layer 1010 overlyingvia 904 provides resistive film 318. In an alternative approach, nitridelayer 1010 is not etched, so that it fully covers via 904 (e.g.,similarly as shown in FIG. 3 ).

In one embodiment, the memory devices discussed herein, including amemory array, may be formed on a semiconductor substrate, such assilicon, germanium, silicon-germanium alloy, gallium arsenide, galliumnitride, etc. In some examples, the substrate is a semiconductor wafer.In other examples, the substrate may be a silicon-on-insulator (SOI)substrate, such as silicon-on-glass (SOG) or silicon-on-sapphire (SOP),or epitaxial layers of semiconductor materials on another substrate. Theconductivity of the substrate, or sub-regions of the substrate, may becontrolled through doping using various chemical species including, butnot limited to, phosphorous, boron, or arsenic. Doping may be performedduring the initial formation or growth of the substrate, byion-implantation, or by any other doping means.

In one embodiment, a transistor discussed herein (e.g., transistor oftransistor circuitry 316) may represent a field-effect transistor (FET)and comprise a three terminal device including a source, drain, andgate. The terminals may be connected to other electronic elementsthrough conductive materials (e.g., metals). In one example, eachtransistor is used in CMOS transistor circuitry formed at the topsurface of a semiconductor wafer and underneath a memory array havingmultiple decks of memory cells. The source and drain may be conductiveand may comprise a heavily-doped (e.g., degenerate) semiconductorregion. The source and drain may be separated by a lightly-dopedsemiconductor region or channel. If the channel is n-type, then the FETmay be referred to as a n-type FET. If the channel is p-type, then theFET may be referred to as a p-type FET. The channel may be capped by aninsulating gate oxide. The channel conductivity may be controlled byapplying a voltage to the gate. For example, applying a positive voltageor negative voltage to an n-type FET or a p-type FET, respectively, mayresult in the channel becoming conductive. A transistor may be on oractivated when a voltage greater than or equal to the transistor’sthreshold voltage is applied to the transistor gate. The transistor maybe off or deactivated when a voltage less than the transistor’sthreshold voltage is applied to the transistor gate.

FIG. 13 shows a method for manufacturing a memory device that implementsspike current suppression, in accordance with some embodiments. Forexample, the method of FIG. 13 can be used to form the split access lineand resistive film of FIG. 3 . In one example, the manufactured memorydevice is memory device 101.

Although shown in a particular sequence or order, unless otherwisespecified, the order of the processes can be modified. Thus, theillustrated embodiments should be understood only as examples, and theillustrated processes can be performed in a different order, and someprocesses can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At block 1301, a via is formed in a memory array. In one example, thevia is via 904. In one example, the memory array is memory array 902.

At block 1303, a resistive film is formed overlying the via. In oneexample, the resistive film is nitride layer 1010.

At block 1305, an access line is formed overlying the resistive film. Inone example, the access line is word line 1012.

At block 1307, a photoresist layer is formed overlying the access line.In one example, the photoresist layer is photoresist layer 1104. In oneexample, the photoresist layer is formed overlying a hard mask (e.g.,hard mask 1102).

At block 1309, the photoresist layer is patterned. In one example, thephotoresist layer is patterned to use in etching that provides opening1202.

At block 1311, the access line is etched using the patterned photoresistlayer to provide first and second portions of the access line. In oneexample, the access line is etched to split the access line into leftand right portions 302, 304.

In one embodiment, a method includes: forming a via (e.g., via 312);forming a resistive film (e.g., 318) overlying the via; forming anaccess line (e.g., an access line that provides left and right portions302, 304) overlying the resistive film; and patterning the access lineto provide first and second portions. The patterning physicallyseparates the first portion from the second portion (e.g., thepatterning provides a split in the access line), and the first portionis configured to access a memory cell (e.g., 308) of a memory array. Afirst section of the resistive film is between the first portion and thevia, and a second section of the resistive film is between the secondportion and the via.

In one embodiment, patterning the access line includes: forming aphotoresist layer overlying the access line; patterning the photoresistlayer; and performing an etch using the patterned photoresist layer toetch the access line. Performing the etch includes etching the accessline to provide a split overlying the via and between the first andsecond portions (e.g., a split located in central region 306 andoverlying via 312).

In one embodiment, performing the etch further includes etching theresistive film to physically separate the first and second sections.

In one embodiment, the first and second sections of the resistive filmeach have a thickness of 1 to 20 nanometers; the first section has awidth of 10 to 200 nanometers; and the second section has a width of 10to 200 nanometers.

In one embodiment, the memory array is part of a memory device (e.g.,101). The method further includes forming a transistor circuit (e.g.,transistor circuitry 316) located under the memory array andelectrically connected to the via. The transistor circuit is configuredto generate a voltage on the first portion to access the memory cellduring a read or write operation, and the voltage is generated inresponse to a command received from a host device (e.g., 126) by acontroller (e.g., 120) of the memory device.

In some embodiments, spike current suppression is implemented by using asocket structure that is formed in an access line (e.g., formed in oneor more word and/or bit lines of a memory array). In some embodiments, asocket of the access line is filled with a conductive layer, and tworesistive films are formed in the access line on each side of theconductive layer (see, e.g., FIG. 14 ). In other embodiments, the socketof the access line is filled with a resistive layer (see, e.g., FIGS.23-24 ), and the conductive layer and two resistive films are not used.

In some embodiments, use of the socket structure above in a memory arraycan be combined with use of the split access line structure as describedabove (e.g., as described for FIGS. 1-13 ). In one embodiment, the sameaccess line may use both the split access line structure and the socketstructure at various points in the access line. In other embodiments,each type of structure can be used on different access lines.

In one embodiment, a memory device includes a memory array. The memoryarray includes access lines. Each of one or several access lines can beconfigured to access memory cells of the memory array, the access linehaving a first portion and a second portion on opposite sides of theaccess line. The first portion is configured to access a first memorycell, and the second portion is configured to access a second memorycell. A conductive layer is located between the first portion and thesecond portion. The conductive layer electrically connects the firstportion to the second portion. A first resistor (e.g., a first resistivefilm integrated into the access line as a spacer) is located between thefirst portion and the conductive layer. A second resistor (e.g., asecond resistive film integrated into the access line as a spacer) islocated between the second portion and the conductive layer. One or morevias are located underlying the conductive layer, and electricallyconnected by the conductive layer to the first and second portions ofthe access line.

In one embodiment, each of one or more access lines has a first portionand a second portion (e.g., left and right portions of a word line). Thefirst portion is configured to access a first memory cell of a memoryarray (e.g., on a left side of the array). The second portion isconfigured to access a second memory cell of the memory array (e.g., ona right side of the array). A conductive layer is located between thefirst and second portions of the access line and has been formed in asocket of the access line. A first resistive film (e.g., tungstensilicon nitride) is integrated into the access line between the firstportion and the conductive layer. A second resistive film (e.g.,tungsten silicon nitride) is integrated into the access line between thesecond portion and the conductive layer. One or more vias areelectrically connected through the conductive layer to the first andsecond portions of the access line.

FIG. 14 shows an access line 1415 having two resistive films 1420, 1422.A conductive layer 1430 has been formed in a socket (see, e.g., socket1702 of FIG. 17 below) of access line 1415, to implement spike currentsuppression, in accordance with some embodiments. Access line has a leftportion 1402 and a right portion 1404 located on opposite sides ofaccess line 1415. Conductive layer 1430 is located between left andright portions 1402, 1404. Conductive layer 1430 is, for example,tungsten. Resistive film 1420 is located between left portion 1402 andconductive layer 1430. Resistive film 1422 is located between rightportion 1404 and conductive layer 1430.

The material used to form resistive films 1420, 1422 has a higherresistivity than the material used to form left and right portions 1402,1404. In one example, left and right portions 1402, 1404 are formed oftungsten. In one example, resistive films 1420, 1422 are formed oftungsten silicon nitride.

A via 1412 is located underlying conductive layer 1430. Conductive layer1430 electrically connects via 1412 to left and right portions 1402,1404. Transistor circuitry 1416 (e.g., a driver) is electricallyconnected to via 1412. In one embodiment, transistor circuitry 1416 isformed in semiconductor substrate 1414, which is located underlying amemory array including memory cells 1408, 1410.

Left portion 1402 is used to access memory cell 1408. Right portion 1404is used to access memory cell 1410. Transistor circuitry 1416 generatesone or more voltages that are applied to access line 1415 through via1412. The voltages are applied to access one or more memory cells usingaccess line 1415. In one embodiment, access to the memory cells isaccomplished in conjunction with applying one or more voltages to bitlines (not shown) of the memory array.

In one example, memory cells 1408, 1410 are similar to memory cells 110,112, memory cells 206, 208, memory cells 402, 404, or memory cell 401.In one example, each access line 1415 is one of access lines 130. In oneexample, transistor circuitry 1416 is similar to transistor circuitry316.

In one embodiment, additional resistive films can be integrated intoaccess line 1415. In one embodiment, access line 1415 has an additionalportion (not shown) electrically connected to left portion 1402 by anadditional resistive film (not shown). For example, the additionalportion and the additional resistive film are located to the left ofmemory cell 1408. In one example, each side of access line 1415 onopposite sides of via 1412 can have multiple portions separated bymultiple resistive films (not shown).

In other embodiments, a signal line (not shown) of a memory or othersemiconductor device can have multiple portions (e.g., tungstenportions) separated by multiple resistive films (e.g., WSiN) such as theresistive films described above.

In one embodiment, the thickness of resistive films 1420, 1422 can bevaried to control the magnitude of the resistance. In one embodiment,each resistive film 1420, 1422 has a different thickness. In oneexample, the thickness is selected to correspond to a characteristic ofthe respective portion of the access line 1415, and/or a respectivecharacteristic of a particular region of the memory array, and/or arespective characteristic of memory cells accessed by the portion of theaccess line.

In one embodiment, an apparatus includes: a memory array including anaccess line (e.g., 1415, 1612) configured to access memory cells (e.g.,1408, 1410) of the memory array, the access line having a first portion(e.g., left portion 1402) and a second portion (e.g., right portion1404) on opposite sides of the access line, where the first portion isconfigured to access a first memory cell, and the second portion isconfigured to access a second memory cell; a conductive layer (e.g.,1430) between the first portion and the second portion, where theconductive layer electrically connects the first portion to the secondportion; a first resistor (e.g., 1420) between the first portion and theconductive layer; a second resistor (e.g., 1422) between the secondportion and the conductive layer; and at least one via (e.g., 1412)underlying the conductive layer, and electrically connected by theconductive layer to the first portion and the second portion.

In one embodiment, the apparatus further includes a driver (e.g., adriver of transistor circuitry 1416) electrically connected to the via,where the driver is configured to generate a voltage on the firstportion to access the first memory cell, and to generate a voltage onthe second portion to access the second memory cell.

In one embodiment, the at least one via is a single via; the access lineis a bit line or a word line; and the driver is a bit line driver or aword line driver.

In one embodiment, the first resistor is a first resistive layer on anend of the first portion; and the second resistor is a second resistivelayer on an end of the second portion. The conductive layer is formed ina socket (e.g., 1702) of the access line. The socket is overlying thevia and between the first and second portions of the access line.

In one embodiment, each of the first resistive layer and the secondresistive layer includes tungsten silicon nitride.

In one embodiment, the socket is formed by patterning and removing athird portion of the access line to physically separate the firstportion from the second portion; and prior to removing the thirdportion, the third portion is located between the first portion and thesecond portion.

In one embodiment, the memory array is part of a memory device; theaccess line is associated with a physical address within the memoryarray; and an access operation by a controller of the memory device toselect the first memory cell addresses both the first and secondportions of the access line.

In one embodiment, an apparatus includes: an access line having a firstportion and a second portion, where the first portion is configured toaccess a memory cell of a memory array; a conductive layer between thefirst portion and the second portion; a first resistive film (e.g.,1420, 1902) between the first portion and the conductive layer; a secondresistive film (e.g., 1422, 1904) between the second portion and theconductive layer; and a via electrically connected, by the conductivelayer, to the first portion and the second portion.

In one embodiment, the apparatus further includes a driver electricallyconnected to the via, where the driver is configured to generate avoltage on the first portion to access the memory cell.

In one embodiment, the conductive layer is located in a socket betweenthe first portion and the second portion; and the socket is formed byremoving a third portion of the access line to physically separate thefirst portion of the access line from the second portion.

In one embodiment, a material forming each of the first resistive filmand the second resistive film has a higher resistivity than a materialforming the first and second portions of the access line.

In one embodiment, each of the first and second resistive films includesat least one of: tungsten silicon nitride; titanium silicide nitride;tungsten nitride; titanium nitride; tungsten silicide; or cobaltsilicide.

In one embodiment, each of the first and second portions is configuredto access memory cells located above and below the respective portion.

In one embodiment, the memory array has a cross-point architecture, andthe memory cell is: a memory cell including chalcogenide; a memory cellincluding a select device, and a phase change material as a memoryelement; a self-selecting memory cell including chalcogenide; or aresistive memory cell.

In one embodiment, the apparatus further includes a driver connected tothe via, where: the access line further has a third portion located atan end of the access line, and overlying or underlying the memory cell;the apparatus further includes a third resistive film between the firstportion and the third portion; and the third portion is electricallyconnected to the via by the first portion so that the driver cangenerate a voltage on the third portion for accessing the memory cell.

FIGS. 15-21 show steps in the manufacture of a memory device thatimplements spike current suppression by forming two resistive films inan access line, and a conductive layer in a socket of the access line,in accordance with some embodiments. In one example, the memory deviceis memory device 101.

FIG. 15 shows a memory array 1502 at an intermediate stage ofmanufacture. Memory array 1502 includes various memory cells 1508. Eachmemory cell 1508 includes a memory stack containing various layers ofmaterials (e.g., chalcogenide, phase change material, etc.)corresponding to the memory cell technology that has been chosen for use(see, e.g., FIG. 8 ). Memory cells 1508 are an example of memory cells110, 112; memory cells 206, 208; or memory cells 1408, 1410.

Memory array 1502 includes a via 1504. In some cases, via 1504 can beformed on a pad similar to pad 906. Memory array 1502 as shown in FIG.15 can be formed using conventional manufacturing techniques.

As shown in FIG. 16 , an access line 1612 (e.g., a word line or bitline) is formed overlying a top surface of memory array 1502. In oneexample, access line 1612 is tungsten. Other conductive materials may beused.

An optional nitride layer 1614 is formed overlying access line 1612.Nitride layer 1614 is, for example, a silicon nitride layer. In oneembodiment, nitride layer 1614 is later used as an etch stop. Aphotoresist layer (not shown) is formed overlying nitride layer 1614 touse for patterning both nitride layer 1614 and access line 1612.

As shown in FIG. 17 , nitride layer 1614 and access line 1612 have beenpatterned by, for example, etching using the photoresist layer above.This patterning provides a socket 1702 in access line 1612. Socket 1702has a height 1704 measured from a bottom 1706 of socket 1702 to a topsurface of nitride layer 1614. If nitride layer 1614 is not used, height1704 is measured to a top surface of access line 1612. In variousembodiments, socket 1702 can be filled with a conductive and/orresistive material that electrically connects the left and rightportions of access line 1612. In various embodiments, socket 1702physically separates the left and right portions of access line 1612.

As shown in FIG. 18 , resistive layer 1802 is formed overlying the leftand right portions of nitride layer 1614, the left and right portions ofaccess line 1612, and filling part of the bottom of socket 1702. In oneexample, resistive layer 1802 includes one or more of tungsten siliconnitride, titanium silicide nitride, tungsten nitride, or titaniumnitride. In one example, one or more of tungsten silicide or cobaltsilicide can be alternatively or additionally used. The proportions ofthe foregoing materials can be varied for different memory arrays. Inone example, resistive layer 1802 is formed using a conformal depositionprocess (e.g., for forming sidewall spacers from resistive layer 1802).

As shown in FIG. 19 , resistive layer 1802 has been etched to provideresistive films 1902, 1904 as spacers on sidewalls of the left and rightportions of access line 1612 and nitride layer 1614. In one example,each spacer has a thickness of 1 to 60 nanometers.

As shown in FIG. 20 , a conductive layer 2002 is formed. A portion ofconductive layer 2002 is formed in socket 1702. In one embodiment,conductive layer 2002 is formed of the same material as access line1612. In one example, conductive layer 2002 is tungsten. In one example,conductive layer 2002 is formed by chemical vapor deposition. In oneembodiment, conductive layer 2002 is formed of a different material thanaccess line 1612.

As shown in FIG. 21 , the uppermost part of conductive layer 2002 isremoved by performing chemical mechanical polishing (CMP) using siliconnitride layer 1614 as a stop layer. After performing the CMP, conductiveportion 2102 remains in socket 1702 (e.g., completely filling thesocket, or filling the socket by at least 85 percent by volume).

Subsequent manufacture of the memory device can be performed usingconventional manufacturing techniques.

As mentioned above, access line 1612 is separated into left and rightportions. In one example, these portions correspond to left and rightportions 1402, 1404 of FIG. 14 . Conductive portion 2102 electricallyconnects each of the left and right portions of access line 1612 to via1504 (through resistive films 1902, 1904, which are electrically inseries).

In one embodiment, the memory array of FIG. 15 may be formed on asemiconductor substrate (e.g., substrate 1414 of FIG. 14 ), such assilicon, germanium, silicon-germanium alloy, gallium arsenide, galliumnitride, etc. In some examples, the substrate is a semiconductor wafer.In other examples, the substrate may be a silicon-on-insulator (SOI)substrate, such as silicon-on-glass (SOG) or silicon-on-sapphire (SOP),or epitaxial layers of semiconductor materials on another substrate. Theconductivity of the substrate, or sub-regions of the substrate, may becontrolled through doping using various chemical species including, butnot limited to, phosphorous, boron, or arsenic. Doping may be performedduring the initial formation or growth of the substrate, byion-implantation, or by any other doping means.

In one embodiment, a transistor as used herein (e.g., a transistor oftransistor circuitry 1416 of FIG. 14 ) may represent a field-effecttransistor (FET) and comprise a three terminal device including asource, drain, and gate. The terminals may be connected to otherelectronic elements through conductive materials (e.g., metals). In oneexample, each transistor is used in CMOS transistor circuitry formed atthe top surface of a semiconductor wafer and underneath a memory arrayhaving multiple decks of memory cells.

FIG. 22 shows a method for manufacturing a memory device that implementsspike current suppression by forming two resistive films and aconductive layer in a socket, in accordance with some embodiments. Forexample, the method of FIG. 22 can be used to form socket 1702 of FIG.17 and resistive films 1902, 1904 of FIG. 21 . In one example, themanufactured memory device is memory device 101.

Although shown in a particular sequence or order, unless otherwisespecified, the order of the processes can be modified. Thus, theillustrated embodiments should be understood only as examples, and theillustrated processes can be performed in a different order, and someprocesses can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At block 2201, a via is formed in a memory array. In one example, thevia is via 1412 or 1504. In one example, the memory array is memoryarray 1502.

At block 2203, an access line is formed overlying the via. In oneexample, the access line is access line 1612.

At block 2205, the access line is patterned to provide first and secondportions. The patterning forms a socket. In one example, the socket issocket 1702. In one example, the first and second portions are the leftand right portions of access line 1612.

At block 2207, a first resistive film and a second resistive film areformed. In one example, the first and second resistive films are spacers1902, 1904.

At block 2209, a conductive layer is formed in the socket. In oneexample, the conductive layer is conductive layer 2002.

In one embodiment, a method includes: forming a via (e.g., 1504);forming an access line (e.g., 1612) overlying the via; patterning theaccess line to provide first and second portions of the access line. Thepatterning forms a socket (e.g., 1702) that physically separates thefirst portion and the second portion. The first portion is configured toaccess a memory cell (e.g., 1508) of a memory array. The method furtherincludes: forming a first resistive film (e.g., 1902) on a sidewall ofthe first portion, and a second resistive film (e.g., 1904) on asidewall of the second portion; and forming a conductive layer (e.g.,2002) in the socket. The conductive layer electrically connects each ofthe first and second portions of the access line to the via.

In one embodiment, patterning the access line includes: forming aphotoresist layer overlying the access line; patterning the photoresistlayer; and performing an etch using the patterned photoresist layer toetch the access line, where performing the etch includes etching theaccess line to provide the socket.

In one embodiment, each of the first and second resistive films has athickness of 1 to 60 nanometers.

In one embodiment, the memory array is part of a memory device. Themethod further includes forming a transistor circuit located under thememory array, where the transistor circuit is configured to generate,using an electrical connection to the via, a voltage on the firstportion to access the memory cell during a read or write operation, andthe voltage is generated in response to a command received from a hostdevice by a controller of the memory device.

In one embodiment, the method further includes, prior to patterning theaccess line, forming a silicon nitride layer (e.g., 1614) overlying theaccess line. Patterning the access line to form the socket includesetching a portion of the silicon nitride layer and the access line.

In one embodiment, the method further includes: after forming theconductive layer in the socket, performing chemical mechanical polishingof the conductive layer using the silicon nitride layer as a stop layer.

In one embodiment, the conductive layer is formed by chemical vapordeposition.

In one embodiment, forming the first and second resistive films isperformed by: forming a resistive layer (e.g., 1802) overlying the firstand second portions of the access line, and overlying a bottom of thesocket; and etching the resistive layer (see, e.g., FIG. 19 ) to providethe first and second resistive films as spacers on the respectivesidewalls of the first and second portions of the access line.

FIGS. 23 and 24 show steps in the manufacture of a memory device thatimplements spike current suppression by forming a resistive layer in asocket, in accordance with some embodiments. In one example, the memorydevice is memory device 101.

FIG. 23 shows memory array 1502 at an intermediate stage of manufacture.In one embodiment, memory array 1502 as shown in FIG. 23 can be formedsimilarly as described for FIGS. 15-17 above.

As shown in FIG. 23 , a resistive layer 2302 is formed in socket 1702.Resistive layer 2302 is used to electrically connect each of left andright portions of access line 1612 to via 1504 in the final memorydevice. In one example, resistive layer 2302 includes one or more oftungsten silicon nitride, titanium silicide nitride, tungsten nitride,or titanium nitride. In one example, one or more of tungsten silicide orcobalt silicide can be alternatively or additionally used. Theproportions of the foregoing materials can be varied for differentmemory arrays.

As shown in FIG. 24 , chemical mechanical polishing of resistivematerial 2302 is performed so that resistive portion 2402 remains insocket 1702. Resistive portion 2402 fills socket 1702 to a height 2404.In one embodiment, after the chemical mechanical polishing, resistiveportion 2402 fills at least 50 percent of the volume of socket 1702,where the volume is determined by height 2404 multiplied by an area ofthe bottom surface 1706 of socket 1702 (such as shown in FIG. 17 ).

FIG. 25 shows a method for manufacturing a memory device that implementsspike current suppression by forming a resistive layer in a socket, inaccordance with some embodiments. For example, the method of FIG. 25 canbe used to form resistive layer 2302 of FIG. 23 . In one example, themanufactured memory device is memory device 101.

Although shown in a particular sequence or order, unless otherwisespecified, the order of the processes can be modified. Thus, theillustrated embodiments should be understood only as examples, and theillustrated processes can be performed in a different order, and someprocesses can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At block 2501, a via is formed in a memory array. In one example, thevia is via 1504. In one example, the memory array is memory array 1502.

At block 2503, an access line is formed overlying the via. In oneexample, the access line is access line 1612.

At block 2505, the access line is patterned to provide first and secondportions. The patterning forms a socket. In one example, the socket issocket 1702.

At block 2507, a resistive layer is formed in the socket. In oneexample, the resistive layer is resistive layer 2302.

In one embodiment, a method includes: forming a via; forming an accessline overlying the via; patterning the access line to provide first andsecond portions of the access line, where the patterning forms a socketthat physically separates the first portion and the second portion, andwhere the first portion is configured to access a memory cell of amemory array; and forming a resistive layer (e.g., 2302 of FIG. 23 ) inthe socket, where the resistive layer electrically connects each of thefirst and second portions of the access line to the via.

In one embodiment, the resistive layer includes at least one of:tungsten silicon nitride; titanium silicide nitride; tungsten nitride;titanium nitride; tungsten silicide; or cobalt silicide.

In one embodiment, patterning the access line includes: forming aphotoresist layer overlying the access line; patterning the photoresistlayer; and performing an etch using the patterned photoresist layer toetch the access line, where performing the etch includes etching theaccess line to provide the socket.

In one embodiment, the method further includes forming a driverunderlying the memory array, where the driver is electrically connectedto the via and configured to generate a voltage on the first portion ofthe access line for accessing the memory cell during a read or writeoperation.

In one embodiment, the method further includes: after forming theresistive layer in the socket, performing chemical mechanical polishingof the resistive layer. After the chemical mechanical polishing, theresistive layer fills at least 50 percent of a volume of the socket.

In some embodiments, spike current suppression is implemented by one ormore charge screening structures that are formed into one or more accesslines of a memory array. Each charge screening structure includes aninsulating layer that splits the access line into top and bottomportions, each electrically isolated from the other by the insulatinglayer (e.g., a thin insulator located in the middle of the access line).This increases the electrical resistance to memory cells of the memoryarray that are located above and/or below one of the insulating layers.For example, the increased resistance forms a resistive bottleneck thatchokes charge flowing from parasitic capacitances of the memory arraythat might otherwise damage a memory cell that has been selected. In oneexample, the insulating layer is an oxide.

In some embodiments, the use of one or more charge screening structureshaving insulating layers in the access line as described herein can becombined with use of the split access line structure as described above(e.g., as described for FIGS. 1-13 ), and/or use of the socket structureas described above (e.g., as described for FIGS. 14-25 ). In oneembodiment, the same access line may use charge screening structures,the split access line structure, and/or the socket structure at variouspoints in the access line. In other embodiments, each type of structurecan be used on different access lines.

In one embodiment, a memory device includes a memory array. The memoryarray includes access lines. Each of one or several access lines can beconfigured to access memory cells of the memory array, the access linehaving a first portion and a second portion on opposite sides (e.g.,left and right sides) of the access line. The first portion isconfigured to access a first memory cell, and the second portion isconfigured to access a second memory cell. Each of the first and secondportions includes one or more charge screening structures.

In one embodiment, the charge screening structures are implemented asvarious screening portions located along the access line. A firstscreening portion of the access line is located in an electrical pathbetween the far memory cells accessed by the first portion and thevia(s). The first screening portion has a first insulating layer in aninterior region (e.g., an oxide layer in the middle) of the access line(e.g., on a left side of the array). A second screening portion of theaccess line is located in an electrical path between the far memorycells accessed by the second portion and the via(s). The secondscreening portion has a second insulating layer in an interior region ofthe access line (e.g., on a right side of the array). Each screeningportion increases a resistance of an electrical path to the near memorycells located above or below one of the insulating layers, so that spikecurrent is suppressed.

FIG. 26 shows an access line 2602 having charge screening structuresthat are used for spike current suppression, in accordance with someembodiments. The charge screening structures include screening portions2608, 2611. Each screening portion 2608, 2611 has a respectiveinsulating layer 2610, 2612 that splits the access line 2602 into anupper or top portion (e.g., 2660) and a lower or bottom portion (e.g.,2662). The upper portion in effect provides an upper resistor, and thelower portion in effect provides a lower resistor. The upper and lowerresistors increase the resistance of the electrical path used to accessnear memory cells above and below the insulating layer 2610, 2612. Forexample, the resistance of each upper and lower resistor as used toaccess one of these near memory cells is greater than a resistance of acomparable length of the conductive portion of access line 2602 used toaccess far memory cells that are not located overlying or underlying aninsulating layer.

Other portions of access line 2602 include conductive portions 2604,2606 on opposite sides of access line 2602. Conductive portion 2604 is,for example, located near distal end 2601 of access line 2602.

Access line 2602 is used to access various memory cells within a memoryarray. In one example, the memory array is memory array 102 of FIG. 1 .These memory cells include, for example, memory cells 2640, 2642, 2644,2646. Near memory cells 2644, 2646 are located underlying insulatinglayers 2610, 2612. Far memory cells 2640, 2642 are located in portionsof access line 2602 that do not contain any such insulating layer.Although not shown, other memory cells can be located overlyinginsulating layers 2610, 2612 (e.g., in a deck of the memory array aboveaccess line 2602).

Access line 2602 includes a central conductive portion 2613. Via 2654 islocated underlying central conductive portion 2613, which electricallyconnects via 2654 to screening portions 2608, 2611 and conductiveportions 2604, 2606. An optional resistive layer 2630 is located betweenvia 2654 and access line 2602. In one example, resistive layer 2630 isformed of tungsten silicon nitride (WSiN).

Via 2654 is electrically connected to transistor circuitry 2650.Transistor circuitry 2650 includes one or more drivers used to generatevoltages on access line 2602 for accessing various memory cells.Transistor circuitry 2650 is formed at a surface of semiconductorsubstrate 2652. In one example, transistor circuitry 2650 is implementedusing bias circuitry 124 of FIG. 1 . In one example, semiconductorsubstrate 2652 is similar to semiconductor substrate 314 of FIG. 3 .

In one embodiment, an apparatus includes: a memory array includingmemory cells (e.g., 2640, 2642, 2644, 2646); an access line (e.g., 2602)configured to access the memory cells, the access line having a firstconductive portion (e.g., 2604) and a second conductive portion (e.g.,2606) on opposite sides of the access line; at least one viaelectrically connected to the first conductive portion and the secondconductive portion; a first screening portion (e.g., 2608) of the accessline, the first screening portion located in an electrical path betweenthe first conductive portion and the via, and the first screeningportion including a first insulating layer (e.g., 2610) in an interiorregion of the access line; and a second screening portion (e.g., 2611)of the access line, the second screening portion located in anelectrical path between the second conductive portion and the via, andthe second screening portion including a second insulating layer (e.g.,2612) in an interior region of the access line.

In one embodiment, the first screening portion further includes a firstupper resistor above the first insulating layer, and a first lowerresistor below the first insulating layer; and the second screeningportion further includes a second upper resistor (e.g., 2660) above thesecond insulating layer, and a second lower resistor (e.g., 2662) belowthe second insulating layer.

In one embodiment, the access line is formed by placing a top conductivelayer overlying a bottom conductive layer; the first upper resistor is aportion of the top conductive layer overlying the first insulatinglayer; and the first lower resistor is a portion of the bottomconductive layer underlying the first insulating layer.

In one embodiment, a first memory cell accessed by the access line islocated underlying or overlying the first insulating layer, and a secondmemory cell accessed by the access line is located underlying oroverlying the second insulating layer.

In one embodiment, the apparatus further includes a central conductiveportion (e.g., 2613) of the access line located between the firstconductive portion and the second conductive portion. The via is locatedunderlying the central conductive portion; and the first insulatinglayer and the second insulating layer do not extend into the centralconductive portion.

In one embodiment, the apparatus further includes a resistive layer(e.g., 2630) between the via and the central conductive portion.

In one embodiment, the resistive layer includes tungsten siliconnitride.

In one embodiment, each of the first insulating layer and the secondinsulating layer has a thickness of 1 to 15 nanometers.

In one embodiment, the at least one via is a single via; and the accessline is a bit line.

In one embodiment, the memory array is part of a memory device; and anaccess operation by a controller of the memory device to select thefirst memory cell addresses both the first and second conductiveportions of the access line.

FIG. 27 shows an access line 2702 having insulating layers 2710, 2712,2714 located in interior regions of access line 2702 and used for spikecurrent suppression, in accordance with some embodiments. In oneexample, access line 2702 is similar to access line 2602. Access line2702 includes left portion 2704, right portion 2706, and central portion2713. Left portion 2704 and right portion 2706 are on opposite sides ofcentral portion 2713.

Insulating layers 2710, 2714 are located in interior regions of the leftportion 2704 of access line 2702. Insulating layer 2712 is located in aninterior region of the right portion 2706 of access line 2702.Insulating layer 2714 is spaced apart from insulating layer 2710 andlocated towards distal end 2701 of access line 2702.

In one example, insulating layer 2710 is located in the middle of accessline 2702 (e.g., at a height equal to 40-60 percent of the thickness2711 of access line 2702). In other examples, insulating layer 2710 canbe located at varying (e.g., higher or lower) heights within theinterior of access line 2702 in order to customize the resistance of thetop and bottom portions of access line 2702 located above and belowinsulating layer 2710.

Access line 2702 is used to access memory cells of a memory array (e.g.,memory array 102 of FIG. 1 ). These memory cells include memory cells2740, 2742, 2743, 2744, 2746. For example, memory cell 2740 is locatedoverlying insulating layer 2714. Memory cell 2744 is located underlyinginsulating layer 2714.

Driver 2750 is electrically connected to via 2754. Driver 2750 generatesone or more voltages on access line 2702 when accessing memory cells.Central portion 2713 electrically connects via 2754 to left and rightportions 2704, 2706 of access line 2702.

An optional resistive layer 2730 is located between via 2754 and centralportion 2713. In one example, resistive layer 2730 is similar toresistive layer 2630 of FIG. 26 .

Insulating layer 2712 is located at a height of 2709 above a bottom 2707of access line 2702. Insulating layer 2712 has a central longitudinalaxis 2705. Height 2709 is determined by the distance between bottom 2707and central longitudinal axis 2705. In one example, height 2709 is 30-70percent of thickness 2711 of access line 2702.

In one example, access layer 2702 provides access to memory cellslocated in a deck of the memory array above the access line 2702, and tomemory cells in a deck below the access line 2702. The height 2709 ofinsulating layer 2712 can be adjusted so that insulating layer 2712 ispositioned more closely to the deck that needs more resistancescreening. In one example, a determination is made (e.g., duringmanufacture) of those decks in the memory array that have a greater needof resistance screening and/or susceptibility to spike currents. Inresponse to this determination, the insulating layer 2712 is positionedmore closely to that particular deck(s) to provide increased protectionagainst spike currents.

Insulating layer 2712 has a lateral length 2703. In one example, thelateral length is 50-300 nanometers.

In one embodiment, access line may include one or more resistive layers2760, 2762. In one example, resistive layers 2760, 2762 can be formedsimilarly as described above for resistive films 1420, 1422 of FIG. 14 .

In one embodiment, an apparatus includes: an access line (e.g., 2702)having a first portion (e.g., 2704), a second portion (e.g., 2706), anda central portion (e.g., 2713). The first and second portions are onopposite sides of the central portion, and each of the first and secondportions is configured to access at least one memory cell (e.g., 2743,2746) of a memory array. The access line includes a first insulatinglayer (e.g., 2710) in the first portion and a second insulating layer(e.g., 2712) in the second portion. Each of the first and secondinsulating layers is located in an interior region of the access line.

The apparatus further includes a via (e.g., 2754) electricallyconnected, by the central portion of the access line, to the first andsecond portions of the access line; and a driver (e.g., 2750)electrically connected to the via, wherein the driver is configured togenerate a voltage on the first portion to access a first memory cell(e.g., 2743), the first memory cell located in a portion of the memoryarray underlying or overlying the first insulating layer, and togenerate a voltage on the second portion to access a second memory cell,the second memory cell located in a portion of the memory arrayunderlying or overlying the second insulating layer.

In one embodiment, the access line is configured to access at least1,000 memory cells of the memory array; a first group of 100 to 500memory cells of the memory array is located underlying the firstinsulating layer; and a second group of 100 to 500 memory cells (e.g., agroup including memory cell 2746) of the memory array is locatedunderlying the second insulating layer.

In one embodiment, the access line has a thickness (e.g., 2711), acentral longitudinal axis (e.g., 2705) of the second insulating layer(e.g., 2712) is located at a height (e.g., 2709) above a bottom (e.g.,2707) of the access line, and the height is 30 to 70 percent of thethickness.

In one embodiment, each of the first and second insulating layers has alateral length (e.g., 2703) of 50 to 300 nanometers. For example, thelateral length can be varied to adjust the resistance of the access line2702 as needed to accommodate varying conditions of spike currentdischarge.

In one embodiment, the access line further includes a third insulatinglayer (e.g., 2714) located in an interior region of the first portion ofthe access line, the third insulating layer spaced apart from the firstinsulating layer and towards a distal end (e.g., 2701) of the firstportion; and the voltage generated on the first portion is used toaccess a third memory cell, the third memory cell located in a portionof the memory array underlying or overlying the third insulating layer.

In one embodiment, each of the first and second insulating layersincludes at least one of silicon nitride, an atomic layer deposition(ALD) oxide, or a thermal oxide.

In one embodiment, the memory array has a cross-point architecture.

In one embodiment, the first memory cell is: a memory cell includingchalcogenide; a memory cell including a select device, and a phasechange material as a memory element; a self-selecting memory cellincluding chalcogenide; or a resistive memory cell.

FIGS. 28-32 show steps in the manufacture of a memory device thatimplements spike current suppression by forming one or more chargescreening structures in an access line, in accordance with someembodiments. In one example, the memory device is memory device 101.

FIG. 28 shows a memory array 2802 at an intermediate stage ofmanufacture. Memory array 2802 includes various memory cells 2807, 2809.Each memory cell 2807, 2809 includes a memory stack containing variouslayers of materials (e.g., chalcogenide, phase change material, etc.)corresponding to the memory cell technology that has been chosen for use(see, e.g., FIG. 8 ). Memory cells 2807, 2809 are an example of memorycells 110, 112; memory cells 206, 208; or memory cells 1408, 1410.

Memory array 2802 includes a via 2804. In some cases, via 2804 can beformed on a pad similar to pad 906. Memory array 2802 as shown in FIG.28 can be formed using conventional manufacturing techniques.

As shown in FIG. 28 , a resistive layer 2806 has been formed overlyingmemory array 2802. In one example, resistive layer 2806 is a tungstensilicon nitride layer. In one example, resistive layer 2806 providesresistive layer 2630 of FIG. 26 .

A bottom conductive layer 2808 has been formed overlying resistive layer2806. Bottom conductive layer 2808 has a distal end 2810. In oneexample, distal end 2810 corresponds to distal end 2601 of FIG. 26 or2701 of FIG. 27 . In one example, bottom conductive layer 2808 istungsten. Other conductive materials may be used.

As shown in FIG. 29 , a photoresist layer has been formed overlyingbottom conductive layer 2808. The photoresist layer is patterned toprovide an opening that exposes a portion of bottom conductive layer2808. After patterning, a portion 2902 of the photoresist layer isoverlying a portion of memory cells 2809, and a portion 2904 of thephotoresist layer is overlying via 2804. The exposed portion of bottomconductive layer 2808 is located overlying memory cells 2807.

As shown in FIG. 30 , the exposed portion of bottom conductive layer2808 has been etched using the patterned photoresist layer. This etchingprovides opening 3002 in the top surface of the bottom conductive layer2808. Opening 3002 has, for example, a depth of 1-15 nanometers. In oneexample, the etching is a dry etch process used to remove a fewnanometers of tungsten. The photoresist is stripped in situ.

As shown in FIG. 31 , an insulating layer 3102 has been formed inopening 3002. In one example, the insulating layer 3102 is siliconnitride, an atomic layer deposition oxide, or a thermal oxide. In oneexample, insulating layer 3102 has a thickness of less than 15nanometers. In one example, an oxide is deposited, and chemicalmechanical polishing is performed with a stop on the bottom conductivelayer 2808 (e.g., tungsten). Other types of insulators can be formed inopening 3002. Memory cells 2807 are located underlying insulating layer3102.

As shown in FIG. 32 , a top conductive layer 3202 is formed overlyingbottom conductive layer 2808 and insulating layer 3102. In one example,top conductive layer 3202 is tungsten. In other examples, otherconductive materials can be used.

In one example, insulating layer 3102 provides insulating layer 2610 ofFIG. 26 or insulating layer 2710 of FIG. 27 . In one example, top andbottom conductive layers 3202, 2808 provide access line 2602 or 2702.

In one example, top and bottom conductive layers 3202, 2808 provide abit line for a memory array. In one example, top and bottom conductivelayers 3202, 2808 are used to form other bit lines (not shown) of thememory array. In one example, the other bit lines are formed bypatterning top and bottom conductive layers 3202, 2808.

FIG. 33 shows a cross-sectional view (taken along line AA, asillustrated) of the access line and memory array of FIG. 32 . Asillustrated, various bit lines 3302 have top and bottom portionsseparated by insulating layer 3102. Bit lines 3302 are formed bypatterning top and bottom conductive layers 3202, 2808.

FIG. 34 shows a method for manufacturing a memory device that implementsspike current suppression using one or more charge screening structuresin an access line, in accordance with some embodiments. For example, themethod of FIG. 34 can be used to form the charge screening structures ofFIGS. 26 or 27 . In one example, the manufactured memory device ismemory device 101.

Although shown in a particular sequence or order, unless otherwisespecified, the order of the processes can be modified. Thus, theillustrated embodiments should be understood only as examples, and theillustrated processes can be performed in a different order, and someprocesses can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At block 3401, a memory array including memory cells and one or morevias is formed. In one example, the memory cells are memory cells 2640,2642, 2644, 2646. In one example, the vias include via 2654.

At block 3403, a bottom conductive layer is formed overlying the memorycells in the vias. In one example, the bottom conductive layer is bottomconductive layer 2808.

At block 3405, an opening is formed in a top surface of the bottomconductive layer. In one example, an opening is formed in bottomconductive layer 2808.

At block 3407, an insulating layer is formed in the opening. In oneexample, the insulating layer is insulating layer 3102.

At block 3409, a top conductive layer is formed overlying the insulatinglayer and the bottom conductive layer. In one example, the topconductive layer is top conductive layer 3202.

In one embodiment, a method includes: forming a memory array includingmemory cells and at least one via; forming a first conductive layer(e.g., 2808) overlying the memory cells and the via, wherein the firstconductive layer is electrically connected to the memory cells; formingan opening in a top surface of the first conductive layer; forming aninsulating layer (e.g., 3102) in the opening, wherein a portion of thememory cells are located underlying the insulating layer; and forming asecond conductive layer (e.g., 3202) overlying the insulating layer andthe first conductive layer, wherein the first and second conductivelayers provide an access line for accessing the memory cells.

In one embodiment, the method further includes forming a driver (e.g.,2750) in a semiconductor substrate. The memory array is formed overlyingthe semiconductor substrate, and the driver is electrically connected tothe via. The driver is configured to generate a voltage on the accessline for selecting one or more of the memory cells.

In one embodiment, the method further includes forming a resistive layer(e.g., 2806) between the via and the first conductive layer.

In one embodiment, the method further includes: forming a photoresistlayer overlying the first conductive layer; patterning the photoresistlayer; and etching the first conductive layer using the patternedphotoresist layer to provide the opening in the top surface of the firstconductive layer.

In one embodiment, a first portion (e.g., 2904) of the patternedphotoresist layer is overlying the via, and a second portion (e.g.,2902) of the patterned photoresist layer is overlying a portion of thememory cells located at a distal end (e.g., 2810) of the firstconductive layer.

In one embodiment, the access line is a first one of a plurality of bitlines (e.g., bit lines 3302 of FIG. 33 ), other ones of the bit linesare used to access other memory cells in the memory array, and theplurality of bit lines is formed from the first conductive layer and thesecond conductive layer.

In one embodiment, the formed opening has a depth of 1 to 15 nanometers.

FIG. 35 shows an access line 3502 having multiple insulating layerslocated in an interior region of the access line and used for spikecurrent suppression, in accordance with some embodiments. In oneexample, access line 3502 is access line 2602 or 2702.

Access line 3502 includes various insulating layers arranged in parallelwith respect to a vertical orientation, as illustrated. These insulatinglayers include insulating layer 3510 and 3511. In one example, each ofthe insulating layers is similar to insulating layer 2610 or 2710.

The lateral length of each insulating layer can be varied to customize aresistance of access line 3502 at various points along the access line3502. In one embodiment, varying the lateral length of the insulatinglayers provides a gradient in the resistance of the top and/or bottomportions of access line 3502 that are above or below the insulatinglayers. For example, the resistance of bottom portion 3520 of accessline 3502 that is overlying memory cell 3540 is less (due to a greaterthickness of the conductive material of access line 3502) than theresistance of bottom portion 3521 of access line 3502 that is overlyingmemory cell 3544 (due to a lesser thickness of the conductive materialof access line 3502).

In one example, memory cell 3544, which is nearer to via 2654, is moresusceptible to spike current damage than memory cell 3540, which isfurther away from via 2654. Thus, increased resistance to spike currentdamage is provided by a greater number of overlying insulating layers.Memory cell 3540 is less susceptible to spike current damage, and thushas a lower number of overlying insulating layers.

In various embodiments, the number of insulating layers provided inparallel can vary between two or more as desired. Although only a leftportion of the insulating layers is illustrated as having a gradient,the right portion of the insulating layers may also have a gradient.

In addition, the length of each insulating layer can be varied. It isnot required that the insulating layers be formed to have a symmetricalstructure. In one example, memory cells overlying access line 3502 havea different susceptibility to spike current damage (e.g., due to adifferent type of memory cell or structure), such that the structure ofthe insulating layers closer to the top surface of access line 3502 isdifferent than the structure of the insulating layers closer to thebottom surface of access line 3502.

In one embodiment, the vertical spacing between the insulating layerscan also vary from one layer to another. In one example, the verticalspacing between each insulating layer is 5-30 nanometers.

Various embodiments related to memory devices using a folded access linestructure for spike current suppression when accessing memory cells in amemory array are now described below. The generality of the followingdescription is not limited by the various embodiments described above.

As mentioned above, in some memory arrays (e.g., a cross-point memoryarray), current discharges through a memory cell may result in currentspikes (e.g., relatively high current discharge through the memory cellin a relatively short time period), which may cause damage to the memorycell. In particular, for cross-point memory arrays, spike currentdischarges present a significant reliability risk.

A cross-point memory device typically uses the junction of twoperpendicular metal lines (e.g., word lines and bit lines) to supply thevoltages required to read and write individual memory cells. Some newercross-point memory devices use a quilt architecture in which word lineand bit line drivers are spread across a tile and each cell has aphysical distance from the respective driver (e.g., near the driver, orfar from the driver).

Memory cells having a physical distance closer to a driver are referredto below as near memory cells. Memory cells having a physical distancefarther away from a driver are referred to below as far memory cells.The near memory cells are physically closer to the driver than the farmemory cells.

The severity of spike currents can depend on the physical distance of aparticular memory cell from a driver. In one example, a memory cellincludes a selector device (e.g., using a chalcogenide), a memorydevice, and electrodes. During read operations of the cell, a highpotential is applied to the cell. When the applied voltage is above thethreshold voltage, the selector device snaps. The snapping of theselector device can instantaneously result in a transient spike currentbecause of charge built up in the memory array and periphery circuits.

Depending on the magnitude of the spike current, the memory device mayundesirably change its state from set to reset. This can cause thetechnical problem of erroneous and/or unreliable data storage for amemory device. The spike current exponentially increases with highercurrent delivery. Thus, near memory cells with higher current delivery(e.g., because of the proximity of CMOS circuit drivers) are moresignificantly impacted by the spike current as compared to far memorycells.

In some cases, the impact of spike current is noticed during the setread disturb test (a test for reading written cells) at probe. Thisresults in lower wafer yield performance.

Spike mitigation sometimes can be achieved by reducing capacitanceand/or increasing resistance. Lowering the capacitance might be achievedby moving to lower resistance metal layers and/or making architecturalchanges. However, such changes typically need significant developmentand integration work.

Increasing the resistance can be achieved in various ways. Some methodschange one of the materials in the memory cell. Examples includenitrogen incorporation in electrodes, multi-layer WSiN/carbon, andelectrode modifications. However, changing the memory cell stack itselfcan impact performance and/or reliability in some cases.

To address technical problems associated with spike currents, variousembodiments described below increase the resistance of the electricalpath between memory cells and the drivers (e.g., CMOS drivers) thatgenerate voltages on access lines used to access the memory cells. Inone embodiment, top and bottom insulating layers are integrated into anaccess line (e.g., metal word line) to provide a folded structure thatincreases a length of an electrical path used to connect a driver tonear memory cells accessed using the access line.

In an alternative embodiment, highly-resistive layers can be usedinstead of the insulating layers above. The layers are sufficientlyresistive that the resistance of the electrical path to the near memorycells remains high so as to suppress spike currents.

In one embodiment, a memory device (e.g., having a cross-point memoryarray), uses access lines for accessing memory cells of a memory array.Each access line is formed of a conductive material (e.g., tungsten).Memory cells are generally located underlying or overlying eachrespective access line used to select the cells.

Each access line has a structure that includes a top portion, a middleportion and a bottom portion. The middle portion is located underlyingthe top portion. The bottom portion is located underlying the middleportion.

A top insulating layer is located at least partially underlying the topportion and overlying the middle portion. A bottom insulating layer islocated underlying the middle portion and at least partially overlyingthe bottom portion.

A via is electrically connected to the middle portion, and a driver iselectrically connected to the via. The driver is configured to generatea voltage on the access line to access the memory cells.

In one embodiment, the above access line structure is configured at theend of each access line that is closest to the respective via thatconnects the memory cells to be selected to a respective driver(s). Thisstructure is located at the end of the access line that is underlying oroverlying the near memory cells so that the electrical path to the nearmemory cells has a greater resistance than would be the case in theabsence of the top and bottom insulating layers. The other end of theaccess line that is used to access far memory cells does not have thisaccess line structure. Also, the electrical path to the far memory cellshas a greater physical length such that spike current discharge istypically not a significant concern for these far cells.

The positioning of the insulating layers relative to the top, middle,and bottom portions of the access line results in a meandering, foldedelectrical path in the access line from the driver, through the via, tothe near memory cells (cells closest to the driver). This meanderingprovides the folded access line structure. For example, in thisstructure, the electrical current flows to a near memory cell in a firstdirection through the middle portion, and but flows in an opposite,second direction through the top or bottom portion (depending on whethera top or bottom memory cell is being accessed). In one example, thefirst and second direction are different by 180 degrees.

One advantage of the folded access line structure is that it extends theeffective access line length to the near memory cells. In other words,the folded structure causes the length of the electrical path to nearmemory cells to be longer. As a result, the length of the electricalpath to each of the near cells and to each of the far cells is closer invalue (there is less dispersion in the lengths). The conductive portionof the access line is also thinner (the middle portion of the foldedstructure above) so that the resistance is higher, which increases thetotal resistance in the circuit path to the memory cells.

In one example for a cross-point memory array, the electrical resistanceon the circuit path to the near cells is increased by about 2 to 4 timesas compared to the resistance that would be present in the absence ofthe top and bottom insulating layers that provide the folded structure.Thus, the electrical resistance on the circuit path to the near cellscan be configured to be roughly comparable to the resistance on thecircuit path to the far cells.

In one example, each of the top and bottom insulating layers in theabove folded structure can be formed of a material similarly as used toform respective insulating layers 2610, 2612 of FIG. 26 .

In one embodiment, the insulating layer is replaced by ahighly-resistive layer. For example, the highly-resistive layer isformed of a material that has a resistivity that is at least 100 timesgreater than the resistivity of the material used to form the conductiveportions of the access line.

In one embodiment, the vertical spacing between the top and bottominsulating layers can be varied (e.g. varied for different access linesin a memory array, such as based on the type of memory cell and/orconfigurable operating mode of the memory cell). In one example, thevertical spacing between each insulating layer is at least 5 nanometers(e.g., 20-100 nanometers). Also, it is not required that the top,middle, and bottom portions of the access line have equal thicknesses.

Another advantage of the folded access line structure is that largertile sizes can be used. A cross-point memory array is often configuredusing tiles. Each tile may have, for example, a size of 4,000 by 4,000memory cells. Using prior approaches, increasing the tile size couldincrease spike discharge currents to unacceptable levels. However, useof the folded structure above permits larger tile sizes, while keepingspike discharge to acceptable levels. In one example, a tile usingfolded access line structures could have a size of 6,000 by 6,000 memorycells.

Another advantage provided by the folded access line structure is thatthe access line modifies the resistance outside the memory cell stack,which has less trade-off with other cell performance and reliabilitycompared to modifying the elements in the cell stack.

Another advantage is that use of the top and bottom insulating layersincreases the physical length of the discharge path from memory cellsabove the access line to memory cells below (e.g., directly below) theaccess line. For example, when a near memory cell below the access linesnaps, the discharge path from memory cells on top of the access line tothe snapped cell on the bottom of the access line is longer because ofthe meandering folded path provided by the folded access line structureabove. This reduces the magnitude of the discharge current.

Other advantages include that leakage is not higher as compared to priorapproaches when using the folded structure, and no added space isrequired to form the folded structure in the memory array. This isbecause the insulating layers are formed within the interior of theaccess line. Also, the folded access line structure above is not limitedto use in cross-point memory devices, but can also be used in othersemiconductor devices that use metal lines.

FIG. 36 shows a folded access line structure used for spike currentsuppression in a memory array of a memory device, in accordance withsome embodiments. Only a portion of the memory array is illustrated forsimplicity. Only certain features of the memory array are shown for easeof illustration. In one example, the memory array can be implemented aspart of memory array 102 of FIG. 1 .

Access line 3602 is used to access various memory cells in the memoryarray. These cells include cells located overlying and underlying accessline 3602. For example, near memory cells 3620, 3630 are underlyingaccess line 3602. Near memory cells 3622, 3628 are overlying access line3602.

In another example, far memory cells 3626, 3634 are underlying accessline 3602. Far memory cells 3624, 3632 are overlying access line 3602.

It should be noted that each representative memory cell rectangle asillustrated in FIG. 36 represents, in an actual memory device, a groupof cells. For example, memory cells 3620 may correspond to 100 to 1,000memory cells. As another example, each rectangle as shown for memorycells 3630, 3622, 3628 may correspond to hundreds or thousands of memorycells. Similarly, each rectangle as shown for memory cells 3626, 3634,3624, 3632 may correspond to hundreds or thousands of memory cells.

Access line 3602 is formed of a conductive material. In one example theconductive material is tungsten. Other metals can be used.

Access line 3602 includes a top portion having left and right sides3604, 3610, a middle portion having left and right sides 3608, 3612, anda bottom portion having left and right sides 3606, 3614. The left andright sides of access line 3602 may be formed symmetrically, or may beasymmetrically varied (e.g., left and right sides are asymmetric fordesign reasons particular to certain memory cells).

Top insulating layer 3638 is partially underlying top portion left side3604 and top portion right side 3610. Top insulating layer 3638 isoverlying middle portion left side 3608 and middle portion right side3612. Top insulating layer 3638 extends in a horizontal direction awayfrom via 3650 to the left and right sides of access line 3602 to extendunder the near memory cells, but does not extend so far as to be underthe far memory cells.

A bottom insulating layer has left side 3618 and right side 3619. Leftside 3618 is underlying middle portion left side 3608, and partiallyoverlying bottom portion left side 3606. Bottom insulating layer rightside 3619 is underlying middle portion right side 3612, and partiallyoverlying bottom portion right side 3614. The bottom insulating layer isnot located overlying via 3650.

Via 3650 is electrically connected to middle portion left side 3608 andmiddle portion right side 3612. Central part 3616 of the middle portionof access line 3602 extends over via 3650 and connects the left andright sides of the middle portion. Central part 3616 electricallyconnects the middle portion to via 3650 to provide a conductiveelectrical path from via 3650 to left and right sides 3608, 3612.

A driver (not shown) is electrically connected to via 3650. The driveris configured to generate a voltage on access line 3602 to access thememory cells. The voltage is generated by current that flows throughmiddle portion left side 3608 and middle portion right side 3612 to theleft and right sides of access line 3602.

In one example, the driver is configured in bias circuitry 124 of FIG. 1. In one example, access line 3602 is one of access lines 130 of FIG. 1. In one example, via 3650 is one of vias 134. In one example, thedriver is driver 2750 of FIG. 27 . In one example, the memory cells ofFIG. 36 are implemented using the cell structure as used for memorycells 2640, 2642, 2644, 2646 of FIG. 26 .

Access line 3602 is configured to have a central region 3640, nearregions 3641, 3643, and far regions 3642, 3644. The top portion ofaccess line 3602 is located on opposite sides of central region 3640.The top portion is not located overlying via 3650.

The top and bottom insulating layers extend throughout and are locatedin near regions 3641, 3643. The top and bottom insulating layers do notextend to and are not located in far regions 3642, 3644. Thus, the topand bottom insulating layers block electrical current flow for the nearmemory cells in near regions 3641, 3643 (e.g., near cells 3628), but notfor the far memory cells in far regions 3642, 3644 (e.g., far cells3632).

The top insulating layer also extends through and across central region3640. The top insulating layer is overlying central part 3616 of themiddle portion of access line 3602, and is overlying via 3650.

In one embodiment, each of the top and bottom insulating layers isformed from silicon nitride, an atomic layer deposition (ALD) oxide,and/or a thermal oxide.

In one example, the top insulating layer is underlying at least 30percent of the memory cells located overlying access line 3602. Forexample, memory cells 3604, 3628 can represent 1,000 memory cells, andmemory cells 3624, 3632 can represent 1,000 memory cells. Thus, the topinsulating layer is underlying 50 percent of the memory cells locatedoverlying access line 3602. In one example, the bottom insulating layeris similarly overlying at least 30 percent of the memory cells locatedunderlying access line 3602.

The thicknesses of the top portion, middle portion, and bottom portionof access line 3602 can be varied for particular implementations. Forexample, the thickness of the middle portion overlying the bottominsulating layer can be greater than the thickness of the top and/orbottom portion. For example, the thickness of the top portion overlyingthe top insulating layer can be greater than the thickness of the middleportion.

Access line 3602 does not include top and bottom insulating layers infar regions 3642, 3644. Thus, the thickness of access line 3602 in farregions 3642, 3644 is greater than a thickness of the middle portion ofaccess line 3602 in near regions 3641, 3643. In one example, thethickness of access line 3602 in far regions 3642, 3644 is at least 40percent greater than the thickness of the middle portion in near regions3641, 3643.

The use of the top and bottom insulating layers in the folded accessline structure as illustrated in FIG. 36 increases the resistance of theelectrical path from the driver to the near memory cells. This increasedresistance is due to the top and bottom portions being electricallyisolated from via 3650 other than through the middle portion left andright sides 3608, 3612.

In one example, the resistance of the electrical path from the driver tothe near memory cells (e.g., 3622) overlying the top insulating layer iswithin 50 percent of the resistance of the electrical path from thedriver to the far memory cells (e.g., 3624) not overlying the topinsulating layer.

In an alternative embodiment, the top and bottom insulating layers abovecan be replaced by top and bottom resistive layers. Each of the top andbottom resistive layers is formed of a material so that the top andbottom resistive layers each have a resistivity at least 100 timesgreater than a resistivity of the conductive material used to formaccess line 3602. The structure of the memory array is otherwise similarto that described above.

In one example, each of the top resistive layer and the bottom resistivelayer has a thickness of 1 to 20 nanometers. In one example, access line3602 is formed by sputtering or chemical vapor deposition (CVD) oftungsten.

The memory cells can have various structures. In one embodiment, eachmemory cell includes a memory stack containing various layers ofmaterials (e.g., chalcogenide, phase change material, etc.)corresponding to the memory cell technology that has been chosen for use(see, e.g., FIG. 8 ).

In one example, access line 3602 provides a bit line or a word line fora cross-point memory array.

In one embodiment, access line 3602 is formed by deposition of first,second, and third conductive films (e.g., tungsten CVD). The firstconductive film is deposited overlying the via, the second conductivefilm is deposited overlying the first conductive film, and the thirdconductive film is deposited overlying the second conductive film. Afterthe depositions and other manufacturing processing, the bottom portionof access line 3602 is provided by the first conductive film. The middleportion of access line 3602 is provided by the second conductive film,and the top portion of access line 3602 is provided by the thirdconductive film.

FIGS. 37-45 show steps in an approach for the manufacture of a memorydevice that implements spike current suppression using a folded accessline structure in a memory array, in accordance with some embodiments.In one example, these steps are used to manufacture the memory arrayillustrated in FIG. 36 .

FIG. 37 shows a memory array of a memory device at an intermediate stageof manufacture. Via 3702 has been formed in insulating film 3706.Although not shown, various memory cells (e.g., cells 3620, 3626) areformed in insulating film 3706. Conductive film 3704 is formed overlyingvia 3702 and insulating film 3706.

In one example, conductive film 3704 is formed by tungsten deposition.In one example, insulating film 3706 is silicon oxide and/or other oxidefilm materials.

As shown in FIG. 38 , conductive film 3704 is etched to form openings3802, 3804 on opposite sides of via 3702. In one example, conductivefilm 3704 is patterned and etched using photolithography. Openings 3802,3804 are filled with an oxide or other insulating material, followed bya chemical mechanical polishing (CMP) processing step.

As shown in FIG. 39 , insulating film 3902 is formed overlyingconductive film 3704.

As shown in FIG. 40 , insulating film 3902 is patterned and etched. Theetching forms opening 4002 overlying via 3702, and forms openings 4004that expose a portion of conductive film 3704. In one example,insulating film 3902 is patterned using photolithography.

As shown in FIG. 41 , conductive film 4102 is formed overlyinginsulating film 3902. Conductive film 4102 contacts and electricallyconnects to conductive film 3704 through openings 4002, 4004. In oneexample, conductive film 4102 is formed by tungsten deposition.

As shown in FIG. 42 , insulating film 4202 is formed overlyingconductive film 4102.

As shown in FIG. 43 , insulating film 4202 is patterned and etched toprovide openings 4302 that expose a portion of conductive film 4102. Inone example, insulating film 4202 is patterned using photolithography.

As shown in FIG. 44 , conductive film 4402 is formed overlyinginsulating film 4202. Conductive film 4402 contacts and electricallyconnects to conductive film 4102 through openings 4302.

As shown in FIG. 45 , conductive film 4402 is patterned and etched toform opening 4502 overlying via 3702. In one example, conductive film4402 is patterned using photolithography.

Fill material 4504 is formed in opening 4502. Fill material 4504 is anoxide (e.g., silicon oxide) or other insulating material.

Although not illustrated, memory cells are typically formed underlyingconductive film 3704. Some of these memory cells are near cells locatedunderlying insulating film 3902, and some of these memory cells are farcells that are not located underlying insulating film 3902.

Also, although not illustrated, memory cells are also typically formedoverlying conductive film 4402. Some of these memory cells are nearcells located overlying insulating film 4202, and some of these memorycells are far cells that are not located overlying insulating film 4202.

FIGS. 46-53 show steps in another approach for the manufacture of amemory device that implements spike current suppression using a foldedaccess line structure in a memory array, in accordance with someembodiments. In this approach, a folded access line structure that iselectrically similar in operation for suppressing spike currentdischarge as for that of FIG. 36 is provided.

FIG. 46 shows a memory array of a memory device at an intermediate stageof manufacture. Via 4602 has been formed in insulating film 4606.Although not shown, various memory cells (e.g., cells 3620, 3626) areformed in insulating film 4606. Conductive film 4604 is formed overlyingvia 4602 and insulating film 4606.

In one example, conductive film 4604 is formed by tungsten deposition.In one example, insulating film 4606 is silicon oxide and/or other oxidefilm materials.

As shown in FIG. 47 , conductive film 4604 is etched to form openings4702, 4704 on opposite sides of via 4602. In one example, conductivefilm 4604 is patterned and etched using photolithography. Openings 4702,4704 are filled with an oxide or other insulating material, followed bychemical mechanical polishing (CMP).

As shown in FIG. 48 , insulating film 4802 is formed overlyingconductive film 4604.

As shown in FIG. 49 , insulating film 4802 is patterned and etched. Theetching forms opening 4902 overlying via 4602, and forms openings 4904that expose a portion of conductive film 4604. In one example,insulating film 4802 is patterned using photolithography.

As shown in FIG. 50 , conductive film 5002 is formed overlyinginsulating film 4802. Conductive film 5002 contacts and electricallyconnects to conductive film 4604 through openings 4902, 4904. In oneexample, conductive film 5002 is formed by tungsten deposition.

Insulating film 5006 is formed overlying conductive film 5002.Conductive film 5004 is formed overlying insulating film 5006. In oneexample, conductive films 5002, 5004 are formed by tungsten deposition.

As shown in FIG. 51 , openings 5102, 5104 are formed by etching throughfilms 5004, 5006, 5002, and partially etching into film 4604. In oneexample, openings 5102, 5104 are formed by forming a photoresist layer(not shown) overlying conductive film 5004. The photoresist layer ispatterned and openings 5102, 5104 are etched using the openings in thephotoresist layer.

As shown in FIG. 52 , openings 5102, 5104 are filled with a conductivematerial 5202, 5204. In one example, chemical mechanical polishing isused to planarize the top exposed surfaces of conductive film 5004 andconductive material 5202, 5204.

As shown in FIG. 53 , conductive film 5004 is optionally etched to formopening 5301 overlying via 4602 and insulating film 5006. Opening 5301is filled with insulating material 5302, such as an oxide. In oneexample, conductive film 5004 is patterned and etched usingphotolithography.

When manufacturing a memory device where the insulating layer isreplaced by a highly-resistive layer, as described above, the approachesas described for FIGS. 37-45 or FIGS. 46-53 can be used in a similarmanner.

FIG. 54 shows a method for manufacturing a memory device that implementsspike current suppression using a folded access line structure in amemory array, in accordance with some embodiments.

For example, the method of FIG. 54 can be used to form the folded accessline structure in the memory array of FIG. 36 . In one example, themanufactured memory array is used in memory device 101 of FIG. 1 .

Although shown in a particular sequence or order, unless otherwisespecified, the order of the processes can be modified. Thus, theillustrated embodiments should be understood only as examples, and theillustrated processes can be performed in a different order, and someprocesses can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At block 5401, a first conductive film is formed overlying a via. In oneexample, conductive film 3704 is formed overlying via 3702.

At block 5403, the first conductive film is etched to form openings onopposite sides of the via. In one example, conductive film 3704 isetched to form openings 3802, 3804.

At block 5405, a first insulating film is formed overlying the firstconductive film. In one example, insulating film 3902 is formedoverlying conductive film 3704.

At block 5407, a second conductive film is formed overlying the firstinsulating film. In one example, conductive film 4102 is formedoverlying insulating film 3902.

At block 5409, a second insulating film is formed overlying the secondconductive film. In one example, insulating film 4202 is formedoverlying conductive film 4102.

At block 5411, a third conductive film is formed overlying the secondinsulating film. In one example, conductive film 4402 is formedoverlying insulating film 4202.

In one embodiment, an apparatus comprises: an access line (e.g., 3602)for accessing memory cells (e.g., 3628, 3632) of a memory array,wherein: the access line is formed of a conductive material; the memorycells are located underlying or overlying the access line; and theaccess line comprises a top portion (e.g., 3604, 3610), a middle portion(e.g., 3608, 3616, 3612) underlying the top portion, and a bottomportion (e.g., 3606, 3614) underlying the middle portion.

The apparatus further comprises: a top insulating layer (e.g., 3638) atleast partially underlying the top portion and overlying the middleportion; a bottom insulating layer (e.g., 3618, 3619) underlying themiddle portion and at least partially overlying the bottom portion; avia (e.g., 3650) electrically connected to the middle portion; and adriver electrically connected to the via, wherein the driver isconfigured to generate a voltage on the access line to access the memorycells.

In one embodiment, the access line is formed by deposition of a firstconductive film overlying the via, deposition of a second conductivefilm overlying the first conductive film, and deposition of a thirdconductive film overlying the second conductive film; the bottom portionof the access line is provided by the first conductive film; the middleportion of the access line is provided by the second conductive film;and the top portion of the access line is provided by the thirdconductive film.

In one embodiment, each of the top and bottom insulating layerscomprises at least one of silicon nitride, an atomic layer deposition(ALD) oxide, or a thermal oxide.

In one embodiment, the top insulating layer is underlying at least 30percent of the memory cells located overlying the access line.

In one embodiment, the bottom insulating layer is overlying at least 30percent of the memory cells located underlying the access line.

In one embodiment, the memory cells comprise near memory cells overlyingthe access line, and far memory cells overlying the access line; thenear memory cells are physically closer to the driver than the farmemory cells; and the top insulating layer extends in a horizontaldirection away from the via under the near memory cells, and does notextend under the far memory cells.

In one embodiment, the memory cells comprise near memory cellsunderlying the access line, and far memory cells underlying the accessline, wherein the near memory cells are physically closer to the driverthan the far memory cells; and the bottom insulating layer is locatedoverlying the near memory cells, and is not located overlying the farmemory cells.

In one embodiment, the middle portion and the top insulating layer eachextend over the via from a first side of the access line to a secondside of the access line.

In one embodiment, the bottom insulating layer is patterned so that thebottom insulating layer is not located overlying the via.

In one embodiment, a thickness of the middle portion overlying thebottom insulating layer is greater than a thickness of the top or bottomportion.

In one embodiment, a thickness of the top portion overlying the topinsulating layer is greater than a thickness of the middle portion.

In one embodiment, the top portion is located on opposite sides of acentral region in which the via is located, and the top portion is notlocated overlying the via.

In one embodiment, the top and bottom insulating layers are located in anear region (e.g., 3641, 3643) of the access line; the top or bottominsulating layers are not located in a far region (e.g., 3642, 3644) ofthe access line; and a thickness of the access line in the far region isat least 40 percent greater than a thickness of the middle portion inthe near region.

In one embodiment, the top and bottom portions are electrically isolatedfrom the via other than through the middle portion.

In one embodiment, a resistance of an electrical path from the driver toa near memory cell overlying the top insulating layer is within 50percent of a resistance of an electrical path from the driver to a farmemory cell not overlying the top insulating layer.

In one embodiment, an apparatus comprises: an access line configured toaccess memory cells of a memory array, wherein: the access linecomprises a conductive material; the memory cells are located underlyingor overlying the access line; and the access line comprises a topportion, a middle portion underlying the top portion, and a bottomportion underlying the middle portion.

The apparatus further comprises a top resistive layer at least partiallyunderlying the top portion and overlying the middle portion, wherein thetop resistive layer has a resistivity at least 100 times greater than aresistivity of the conductive material; a bottom resistive layerunderlying the middle portion and at least partially overlying thebottom portion, wherein the bottom resistive layer has a resistivity atleast 100 times greater than a resistivity of the conductive material;and a via electrically connected to the middle portion.

In one embodiment, each of the top resistive layer and the bottomresistive layer has a thickness of 1 to 20 nanometers.

In one embodiment, the top and bottom portions are electrically isolatedfrom the via other than through the middle portion.

In one embodiment, the memory array has a cross-point architecture.

In one embodiment, the conductive material is tungsten.

In one embodiment, each of the memory cells is: a memory cell comprisingchalcogenide; a memory cell comprising a select device, and a phasechange material as a memory element; a self-selecting memory cellcomprising chalcogenide; or a resistive memory cell.

In one embodiment, the access line is formed by sputtering or chemicalvapor deposition (CVD) of the conductive material.

In one embodiment, a method comprises: forming a first conductive film(e.g., 3704) overlying a via (e.g., 3702); etching the first conductivefilm to form first openings in the first conductive film on oppositesides of the via; forming a first insulating film (e.g., 3902) overlyingthe first conductive film; forming a second conductive film (e.g., 4102)overlying the first insulating film; forming a second insulating film(e.g., 4202) overlying the second conductive film; and forming a thirdconductive film (e.g., 4402) overlying the second insulating film.

In one embodiment, the first openings (e.g., 3802, 3804) electricallyisolate opposite sides of the first conductive film from the via otherthan through the second conductive film.

In one embodiment, the method further comprises etching the thirdconductive film to form a second opening overlying the second insulatingfilm and the via.

In one embodiment, the second opening electrically isolates oppositesides of the third conductive film from the via other than through thesecond conductive film.

In one embodiment, the method further comprises etching the firstinsulating film to form a second opening overlying the via, wherein thesecond conductive film is electrically connected to the via through thesecond opening.

In one embodiment, the method further comprises: forming first memorycells and second memory cells underlying the first conductive film,wherein the second memory cells are physically farther away from the viathan the first memory cells; and etching the first insulating film toremove a portion of the first insulating film so that the first memorycells are underlying the first insulating film, and the second memorycells are not underlying the first insulating film.

In one embodiment, the method further comprises: forming first memorycells and second memory cells overlying the third conductive film,wherein the second memory cells are physically farther away from the viathan the first memory cells; and etching the second insulating film toremove a portion of the second insulating film so that the first memorycells are overlying the second insulating film, and the second memorycells are not overlying the second insulating film.

In one embodiment, the method further comprises: forming memory cells atleast one of underlying the first conductive film or overlying the thirdconductive film; and forming a driver electrically connected to the via,the driver configured to generate a voltage for accessing the memorycells.

In one embodiment, the method further comprises: after forming the thirdconductive film, forming second openings by etching through the thirdconductive film, the second insulating film, the second conductive film,and at least a portion of the first conductive film.

In one embodiment, the method further comprises filling the secondopenings with a conductive material.

In one embodiment, the method further comprises etching the thirdconductive film to form a third opening overlying the second insulatingfilm and the via.

In one embodiment, the method further comprises: forming a photoresistlayer overlying the third conductive film; forming second openings inthe photoresist layer; and etching the second insulating film throughthe second openings.

The description and drawings are illustrative and are not to beconstrued as limiting. Numerous specific details are described toprovide a thorough understanding. However, in certain instances,well-known or conventional details are not described in order to avoidobscuring the description. References to one or an embodiment in thepresent disclosure are not necessarily references to the sameembodiment; and, such references mean at least one.

Reference in this specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the disclosure. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment, nor are separate or alternative embodimentsmutually exclusive of other embodiments. Moreover, various features aredescribed which may be exhibited by some embodiments and not by others.Similarly, various requirements are described which may be requirementsfor some embodiments but not other embodiments.

In this description, various functions and/or operations of a memorydevice may be described as being performed by or caused by software codeto simplify description. However, those skilled in the art willrecognize what is meant by such expressions is that the functions and/oroperations result from execution of the code by one or more processingdevices, such as a microprocessor, Application-Specific IntegratedCircuit (ASIC), graphics processor, and/or a Field-Programmable GateArray (FPGA). Alternatively, or in combination, the functions andoperations can be implemented using special purpose circuitry (e.g.,logic circuitry), with or without software instructions. Functions canbe implemented using hardwired circuitry without software instructions,or in combination with software instructions. Thus, the techniques arenot limited to any specific combination of hardware circuitry andsoftware, nor to any particular source for the instructions executed bya computing device.

The memory device as described above can include one or more processingdevices (e.g., processing device 116), such as a microprocessor,executing sequences of instructions contained in a memory, such as ROM,volatile RAM, non-volatile memory, cache or a remote storage device.

Routines executed to implement memory operations may be implemented aspart of an operating system, middleware, service delivery platform, SDK(Software Development Kit) component, web services, or other specificapplication, component, program, object, module or sequence ofinstructions (sometimes referred to as computer programs). Invocationinterfaces to these routines can be exposed to a software developmentcommunity as an API (Application Programming Interface). The computerprograms typically include one or more instructions set at various timesin various memory and storage devices in a computer, and that, when readand executed by one or more processors in a computer, cause the computerto perform operations necessary to execute elements involving thevarious aspects.

A computer-readable medium can be used to store software and data whichwhen executed by a computing device causes the device to perform variousmethods for a memory device (e.g., read or write operations). Theexecutable software and data may be stored in various places including,for example, ROM, volatile RAM, non-volatile memory and/or cache.Portions of this software and/or data may be stored in any one of thesestorage devices. Further, the data and instructions can be obtained fromcentralized servers or peer to peer networks. Different portions of thedata and instructions can be obtained from different centralized serversand/or peer to peer networks at different times and in differentcommunication sessions or in a same communication session. The data andinstructions can be obtained in entirety prior to the execution of theapplications. Alternatively, portions of the data and instructions canbe obtained dynamically, just in time, when needed for execution. Thus,it is not required that the data and instructions be on acomputer-readable medium in entirety at a particular instance of time.

Examples of computer-readable media include, but are not limited to,recordable and non-recordable type media such as volatile andnon-volatile memory devices, read only memory (ROM), random accessmemory (RAM), flash memory devices, solid-state drive storage media,removable disks, magnetic disk storage media, optical storage media(e.g., Compact Disk Read-Only Memory (CD ROMs), Digital Versatile Disks(DVDs), etc.), among others. The computer-readable media may store theinstructions. Other examples of computer-readable media include, but arenot limited to, non-volatile embedded devices using NOR flash or NANDflash architectures. Media used in these architectures may includeun-managed NAND devices and/or managed NAND devices, including, forexample, eMMC, SD, CF, UFS, and SSD.

In general, a non-transitory computer-readable medium includes anymechanism that provides (e.g., stores) information in a form accessibleby a computing device (e.g., a computer, mobile device, network device,personal digital assistant, manufacturing tool having a controller, anydevice with a set of one or more processors, etc.). A “computer-readablemedium” as used herein may include a single medium or multiple media(e.g., that store one or more sets of instructions).

In various embodiments, hardwired circuitry may be used in combinationwith software and firmware instructions to implement various functionsof a memory device. Thus, the techniques are neither limited to anyspecific combination of hardware circuitry and software nor to anyparticular source for the instructions executed by a computing device.

Various embodiments set forth herein can be implemented for memorydevices that are used in a wide variety of different types of computingdevices. As used herein, examples of a “computing device” include, butare not limited to, a server, a centralized computing platform, a systemof multiple computing processors and/or components, a mobile device, auser terminal, a vehicle, a personal communications device, a wearabledigital device, an electronic kiosk, a general purpose computer, anelectronic document reader, a tablet, a laptop computer, a smartphone, adigital camera, a residential domestic appliance, a television, or adigital music player. Additional examples of computing devices includedevices that are part of what is called “the internet of things” (IOT).Such “things” may have occasional interactions with their owners oradministrators, who may monitor the things or modify settings on thesethings. In some cases, such owners or administrators play the role ofusers with respect to the “thing” devices. In some examples, the primarymobile device (e.g., an Apple iPhone) of a user may be an administratorserver with respect to a paired “thing” device that is worn by the user(e.g., an Apple watch).

In some embodiments, the computing device can be a computer or hostsystem, which is implemented, for example, as a desktop computer, laptopcomputer, network server, mobile device, or other computing device thatincludes a memory and a processing device. The host system can includeor be coupled to a memory sub-system (e.g., memory device 101) so thatthe host system can read data from or write data to the memorysub-system. The host system can be coupled to the memory sub-system viaa physical host interface. In general, the host system can accessmultiple memory sub-systems via a same communication connection,multiple separate communication connections, and/or a combination ofcommunication connections.

In some embodiments, the computing device is a system including one ormore processing devices. Examples of the processing device can include amicrocontroller, a central processing unit (CPU), special purpose logiccircuitry (e.g., a field programmable gate array (FPGA), an applicationspecific integrated circuit (ASIC), etc.), a system on a chip (SoC), oranother suitable processor.

In one example, a computing device is a controller of a memory system.The controller includes a processing device and memory containinginstructions executed by the processing device to control variousoperations of the memory system.

Although some of the drawings illustrate a number of operations in aparticular order, operations which are not order dependent may bereordered and other operations may be combined or broken out. While somereordering or other groupings are specifically mentioned, others will beapparent to those of ordinary skill in the art and so do not present anexhaustive list of alternatives.

In the foregoing specification, the disclosure has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope as set forth in the following claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative sense rather than a restrictive sense.

What is claimed is:
 1. An apparatus comprising: an access line foraccessing memory cells of a memory array, wherein: the access line isformed of a conductive material; the memory cells are located underlyingor overlying the access line; and the access line comprises a topportion, a middle portion underlying the top portion, and a bottomportion underlying the middle portion; a top insulating layer at leastpartially underlying the top portion and overlying the middle portion; abottom insulating layer underlying the middle portion and at leastpartially overlying the bottom portion; a via electrically connected tothe middle portion; and a driver electrically connected to the via,wherein the driver is configured to generate a voltage on the accessline to access the memory cells.
 2. The apparatus of claim 1, wherein:the access line is formed by deposition of a first conductive filmoverlying the via, deposition of a second conductive film overlying thefirst conductive film, and deposition of a third conductive filmoverlying the second conductive film; the bottom portion of the accessline is provided by the first conductive film; the middle portion of theaccess line is provided by the second conductive film; and the topportion of the access line is provided by the third conductive film. 3.The apparatus of claim 1, wherein each of the top and bottom insulatinglayers comprises at least one of silicon nitride, an atomic layerdeposition (ALD) oxide, or a thermal oxide.
 4. The apparatus of claim 1,wherein the top insulating layer is underlying at least 30 percent ofthe memory cells located overlying the access line.
 5. The apparatus ofclaim 1, wherein the bottom insulating layer is overlying at least 30percent of the memory cells located underlying the access line.
 6. Theapparatus of claim 1, wherein: the memory cells comprise near memorycells overlying the access line, and far memory cells overlying theaccess line; the near memory cells are physically closer to the driverthan the far memory cells; and the top insulating layer extends in ahorizontal direction away from the via under the near memory cells, anddoes not extend under the far memory cells.
 7. The apparatus of claim 1,wherein: the memory cells comprise near memory cells underlying theaccess line, and far memory cells underlying the access line, whereinthe near memory cells are physically closer to the driver than the farmemory cells; and the bottom insulating layer is located overlying thenear memory cells, and is not located overlying the far memory cells. 8.The apparatus of claim 1, wherein the middle portion and the topinsulating layer each extend over the via from a first side of theaccess line to a second side of the access line.
 9. The apparatus ofclaim 1, wherein the bottom insulating layer is patterned so that thebottom insulating layer is not located overlying the via.
 10. Theapparatus of claim 9, wherein a thickness of the middle portionoverlying the bottom insulating layer is greater than a thickness of thetop or bottom portion.
 11. The apparatus of claim 1, wherein a thicknessof the top portion overlying the top insulating layer is greater than athickness of the middle portion.
 12. The apparatus of claim 1, whereinthe top portion is located on opposite sides of a central region inwhich the via is located, and the top portion is not located overlyingthe via.
 13. The apparatus of claim 1, wherein: the top and bottominsulating layers are located in a near region of the access line; thetop or bottom insulating layers are not located in a far region of theaccess line; and a thickness of the access line in the far region is atleast 40 percent greater than a thickness of the middle portion in thenear region.
 14. The apparatus of claim 1, wherein the top and bottomportions are electrically isolated from the via other than through themiddle portion.
 15. The apparatus of claim 1, wherein a resistance of anelectrical path from the driver to a near memory cell overlying the topinsulating layer is within 50 percent of a resistance of an electricalpath from the driver to a far memory cell not overlying the topinsulating layer.
 16. An apparatus comprising: an access line configuredto access memory cells of a memory array, wherein: the access linecomprises a conductive material; the memory cells are located underlyingor overlying the access line; and the access line comprises a topportion, a middle portion underlying the top portion, and a bottomportion underlying the middle portion; a top resistive layer at leastpartially underlying the top portion and overlying the middle portion,wherein the top resistive layer has a resistivity at least 100 timesgreater than a resistivity of the conductive material; a bottomresistive layer underlying the middle portion and at least partiallyoverlying the bottom portion, wherein the bottom resistive layer has aresistivity at least 100 times greater than a resistivity of theconductive material; and a via electrically connected to the middleportion.
 17. The apparatus of claim 16, wherein each of the topresistive layer and the bottom resistive layer has a thickness of 1 to20 nanometers.
 18. The apparatus of claim 16, wherein the top and bottomportions are electrically isolated from the via other than through themiddle portion.
 19. The apparatus of claim 16, wherein the memory arrayhas a cross-point architecture.
 20. The apparatus of claim 16, whereinthe conductive material is tungsten.
 21. The apparatus of claim 16,wherein each of the memory cells is: a memory cell comprisingchalcogenide; a memory cell comprising a select device, and a phasechange material as a memory element; a self-selecting memory cellcomprising chalcogenide; or a resistive memory cell.
 22. The apparatusof claim 16, wherein the access line is formed by sputtering or chemicalvapor deposition (CVD) of the conductive material.
 23. A methodcomprising: forming a first conductive film overlying a via; etching thefirst conductive film to form first openings in the first conductivefilm on opposite sides of the via; forming a first insulating filmoverlying the first conductive film; forming a second conductive filmoverlying the first insulating film; forming a second insulating filmoverlying the second conductive film; and forming a third conductivefilm overlying the second insulating film.
 24. The method of claim 23,wherein the first openings electrically isolate opposite sides of thefirst conductive film from the via other than through the secondconductive film.
 25. The method of claim 23, further comprising etchingthe third conductive film to form a second opening overlying the secondinsulating film and the via.
 26. The method of claim 25, wherein thesecond opening electrically isolates opposite sides of the thirdconductive film from the via other than through the second conductivefilm.
 27. The method of claim 23, further comprising etching the firstinsulating film to form a second opening overlying the via, wherein thesecond conductive film is electrically connected to the via through thesecond opening.
 28. The method of claim 23, further comprising: formingfirst memory cells and second memory cells underlying the firstconductive film, wherein the second memory cells are physically fartheraway from the via than the first memory cells; and etching the firstinsulating film to remove a portion of the first insulating film so thatthe first memory cells are underlying the first insulating film, and thesecond memory cells are not underlying the first insulating film. 29.The method of claim 23, further comprising: forming first memory cellsand second memory cells overlying the third conductive film, wherein thesecond memory cells are physically farther away from the via than thefirst memory cells; and etching the second insulating film to remove aportion of the second insulating film so that the first memory cells areoverlying the second insulating film, and the second memory cells arenot overlying the second insulating film.
 30. The method of claim 23,further comprising: forming memory cells at least one of underlying thefirst conductive film or overlying the third conductive film; andforming a driver electrically connected to the via, the driverconfigured to generate a voltage for accessing the memory cells.
 31. Themethod of claim 23, further comprising: after forming the thirdconductive film, forming second openings by etching through the thirdconductive film, the second insulating film, the second conductive film,and at least a portion of the first conductive film.
 32. The method ofclaim 31, further comprising filling the second openings with aconductive material.
 33. The method of claim 32, further comprisingetching the third conductive film to form a third opening overlying thesecond insulating film and the via.
 34. The method of claim 23, furthercomprising: forming a photoresist layer overlying the third conductivefilm; forming second openings in the photoresist layer; and etching thesecond insulating film through the second openings.